06 May, 2019
1 commit
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This amends commit 10dce8af3422 ("fs: stream_open - opener for
stream-like files so that read and write can run simultaneously without
deadlock") in how position is passed into .read()/.write() handler for
stream-like files:Rasmus noticed that we currently pass 0 as position and ignore any position
change if that is done by a file implementation. This papers over bugs if ppos
is used in files that declare themselves as being stream-like as such bugs will
go unnoticed. Even if a file implementation is correctly converted into using
stream_open, its read/write later could be changed to use ppos and even though
that won't be working correctly, that bug might go unnoticed without someone
doing wrong behaviour analysis. It is thus better to pass ppos=NULL into
read/write for stream-like files as that don't give any chance for ppos usage
bugs because it will oops if ppos is ever used inside .read() or .write().Note 1: rw_verify_area, new_sync_{read,write} needs to be updated
because they are called by vfs_read/vfs_write & friends before
file_operations .read/.write .Note 2: if file backend uses new-style .read_iter/.write_iter, position
is still passed into there as non-pointer kiocb.ki_pos . Currently
stream_open.cocci (semantic patch added by 10dce8af3422) ignores files
whose file_operations has *_iter methods.Suggested-by: Rasmus Villemoes
Signed-off-by: Kirill Smelkov
07 Apr, 2019
1 commit
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…multaneously without deadlock
Commit 9c225f2655e3 ("vfs: atomic f_pos accesses as per POSIX") added
locking for file.f_pos access and in particular made concurrent read and
write not possible - now both those functions take f_pos lock for the
whole run, and so if e.g. a read is blocked waiting for data, write will
deadlock waiting for that read to complete.This caused regression for stream-like files where previously read and
write could run simultaneously, but after that patch could not do so
anymore. See e.g. commit 581d21a2d02a ("xenbus: fix deadlock on writes
to /proc/xen/xenbus") which fixes such regression for particular case of
/proc/xen/xenbus.The patch that added f_pos lock in 2014 did so to guarantee POSIX thread
safety for read/write/lseek and added the locking to file descriptors of
all regular files. In 2014 that thread-safety problem was not new as it
was already discussed earlier in 2006.However even though 2006'th version of Linus's patch was adding f_pos
locking "only for files that are marked seekable with FMODE_LSEEK (thus
avoiding the stream-like objects like pipes and sockets)", the 2014
version - the one that actually made it into the tree as 9c225f2655e3 -
is doing so irregardless of whether a file is seekable or not.See
https://lore.kernel.org/lkml/53022DB1.4070805@gmail.com/
https://lwn.net/Articles/180387
https://lwn.net/Articles/180396for historic context.
The reason that it did so is, probably, that there are many files that
are marked non-seekable, but e.g. their read implementation actually
depends on knowing current position to correctly handle the read. Some
examples:kernel/power/user.c snapshot_read
fs/debugfs/file.c u32_array_read
fs/fuse/control.c fuse_conn_waiting_read + ...
drivers/hwmon/asus_atk0110.c atk_debugfs_ggrp_read
arch/s390/hypfs/inode.c hypfs_read_iter
...Despite that, many nonseekable_open users implement read and write with
pure stream semantics - they don't depend on passed ppos at all. And for
those cases where read could wait for something inside, it creates a
situation similar to xenbus - the write could be never made to go until
read is done, and read is waiting for some, potentially external, event,
for potentially unbounded time -> deadlock.Besides xenbus, there are 14 such places in the kernel that I've found
with semantic patch (see below):drivers/xen/evtchn.c:667:8-24: ERROR: evtchn_fops: .read() can deadlock .write()
drivers/isdn/capi/capi.c:963:8-24: ERROR: capi_fops: .read() can deadlock .write()
drivers/input/evdev.c:527:1-17: ERROR: evdev_fops: .read() can deadlock .write()
drivers/char/pcmcia/cm4000_cs.c:1685:7-23: ERROR: cm4000_fops: .read() can deadlock .write()
net/rfkill/core.c:1146:8-24: ERROR: rfkill_fops: .read() can deadlock .write()
drivers/s390/char/fs3270.c:488:1-17: ERROR: fs3270_fops: .read() can deadlock .write()
drivers/usb/misc/ldusb.c:310:1-17: ERROR: ld_usb_fops: .read() can deadlock .write()
drivers/hid/uhid.c:635:1-17: ERROR: uhid_fops: .read() can deadlock .write()
net/batman-adv/icmp_socket.c:80:1-17: ERROR: batadv_fops: .read() can deadlock .write()
drivers/media/rc/lirc_dev.c:198:1-17: ERROR: lirc_fops: .read() can deadlock .write()
drivers/leds/uleds.c:77:1-17: ERROR: uleds_fops: .read() can deadlock .write()
drivers/input/misc/uinput.c:400:1-17: ERROR: uinput_fops: .read() can deadlock .write()
drivers/infiniband/core/user_mad.c:985:7-23: ERROR: umad_fops: .read() can deadlock .write()
drivers/gnss/core.c:45:1-17: ERROR: gnss_fops: .read() can deadlock .write()In addition to the cases above another regression caused by f_pos
locking is that now FUSE filesystems that implement open with
FOPEN_NONSEEKABLE flag, can no longer implement bidirectional
stream-like files - for the same reason as above e.g. read can deadlock
write locking on file.f_pos in the kernel.FUSE's FOPEN_NONSEEKABLE was added in 2008 in a7c1b990f715 ("fuse:
implement nonseekable open") to support OSSPD. OSSPD implements /dev/dsp
in userspace with FOPEN_NONSEEKABLE flag, with corresponding read and
write routines not depending on current position at all, and with both
read and write being potentially blocking operations:See
https://github.com/libfuse/osspd
https://lwn.net/Articles/308445https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1406
https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1438-L1477
https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1479-L1510Corresponding libfuse example/test also describes FOPEN_NONSEEKABLE as
"somewhat pipe-like files ..." with read handler not using offset.
However that test implements only read without write and cannot exercise
the deadlock scenario:https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L124-L131
https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L146-L163
https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L209-L216I've actually hit the read vs write deadlock for real while implementing
my FUSE filesystem where there is /head/watch file, for which open
creates separate bidirectional socket-like stream in between filesystem
and its user with both read and write being later performed
simultaneously. And there it is semantically not easy to split the
stream into two separate read-only and write-only channels:https://lab.nexedi.com/kirr/wendelin.core/blob/f13aa600/wcfs/wcfs.go#L88-169
Let's fix this regression. The plan is:
1. We can't change nonseekable_open to include &~FMODE_ATOMIC_POS -
doing so would break many in-kernel nonseekable_open users which
actually use ppos in read/write handlers.2. Add stream_open() to kernel to open stream-like non-seekable file
descriptors. Read and write on such file descriptors would never use
nor change ppos. And with that property on stream-like files read and
write will be running without taking f_pos lock - i.e. read and write
could be running simultaneously.3. With semantic patch search and convert to stream_open all in-kernel
nonseekable_open users for which read and write actually do not
depend on ppos and where there is no other methods in file_operations
which assume @offset access.4. Add FOPEN_STREAM to fs/fuse/ and open in-kernel file-descriptors via
steam_open if that bit is present in filesystem open reply.It was tempting to change fs/fuse/ open handler to use stream_open
instead of nonseekable_open on just FOPEN_NONSEEKABLE flags, but
grepping through Debian codesearch shows users of FOPEN_NONSEEKABLE,
and in particular GVFS which actually uses offset in its read and
write handlershttps://codesearch.debian.net/search?q=-%3Enonseekable+%3D
https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1080
https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1247-1346
https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1399-1481so if we would do such a change it will break a real user.
5. Add stream_open and FOPEN_STREAM handling to stable kernels starting
from v3.14+ (the kernel where 9c225f2655 first appeared).This will allow to patch OSSPD and other FUSE filesystems that
provide stream-like files to return FOPEN_STREAM | FOPEN_NONSEEKABLE
in their open handler and this way avoid the deadlock on all kernel
versions. This should work because fs/fuse/ ignores unknown open
flags returned from a filesystem and so passing FOPEN_STREAM to a
kernel that is not aware of this flag cannot hurt. In turn the kernel
that is not aware of FOPEN_STREAM will be < v3.14 where just
FOPEN_NONSEEKABLE is sufficient to implement streams without read vs
write deadlock.This patch adds stream_open, converts /proc/xen/xenbus to it and adds
semantic patch to automatically locate in-kernel places that are either
required to be converted due to read vs write deadlock, or that are just
safe to be converted because read and write do not use ppos and there
are no other funky methods in file_operations.Regarding semantic patch I've verified each generated change manually -
that it is correct to convert - and each other nonseekable_open instance
left - that it is either not correct to convert there, or that it is not
converted due to current stream_open.cocci limitations.The script also does not convert files that should be valid to convert,
but that currently have .llseek = noop_llseek or generic_file_llseek for
unknown reason despite file being opened with nonseekable_open (e.g.
drivers/input/mousedev.c)Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Yongzhi Pan <panyongzhi@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Tejun Heo <tj@kernel.org>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Julia Lawall <Julia.Lawall@lip6.fr>
Cc: Nikolaus Rath <Nikolaus@rath.org>
Cc: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Kirill Smelkov <kirr@nexedi.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
30 Mar, 2019
1 commit
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syzbot is hitting lockdep warning [1] due to trying to open a fifo
during an execve() operation. But we don't need to open non regular
files during an execve() operation, for all files which we will need are
the executable file itself and the interpreter programs like /bin/sh and
ld-linux.so.2 .Since the manpage for execve(2) says that execve() returns EACCES when
the file or a script interpreter is not a regular file, and the manpage
for uselib(2) says that uselib() can return EACCES, and we use
FMODE_EXEC when opening for execve()/uselib(), we can bail out if a non
regular file is requested with FMODE_EXEC set.Since this deadlock followed by khungtaskd warnings is trivially
reproducible by a local unprivileged user, and syzbot's frequent crash
due to this deadlock defers finding other bugs, let's workaround this
deadlock until we get a chance to find a better solution.[1] https://syzkaller.appspot.com/bug?id=b5095bfec44ec84213bac54742a82483aad578ce
Link: http://lkml.kernel.org/r/1552044017-7890-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
Reported-by: syzbot
Fixes: 8924feff66f35fe2 ("splice: lift pipe_lock out of splice_to_pipe()")
Signed-off-by: Tetsuo Handa
Acked-by: Kees Cook
Cc: Al Viro
Cc: Eric Biggers
Cc: Dmitry Vyukov
Cc: [4.9+]
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
22 Aug, 2018
1 commit
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Pull overlayfs updates from Miklos Szeredi:
"This contains two new features:- Stack file operations: this allows removal of several hacks from
the VFS, proper interaction of read-only open files with copy-up,
possibility to implement fs modifying ioctls properly, and others.- Metadata only copy-up: when file is on lower layer and only
metadata is modified (except size) then only copy up the metadata
and continue to use the data from the lower file"* tag 'ovl-update-4.19' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs: (66 commits)
ovl: Enable metadata only feature
ovl: Do not do metacopy only for ioctl modifying file attr
ovl: Do not do metadata only copy-up for truncate operation
ovl: add helper to force data copy-up
ovl: Check redirect on index as well
ovl: Set redirect on upper inode when it is linked
ovl: Set redirect on metacopy files upon rename
ovl: Do not set dentry type ORIGIN for broken hardlinks
ovl: Add an inode flag OVL_CONST_INO
ovl: Treat metacopy dentries as type OVL_PATH_MERGE
ovl: Check redirects for metacopy files
ovl: Move some dir related ovl_lookup_single() code in else block
ovl: Do not expose metacopy only dentry from d_real()
ovl: Open file with data except for the case of fsync
ovl: Add helper ovl_inode_realdata()
ovl: Store lower data inode in ovl_inode
ovl: Fix ovl_getattr() to get number of blocks from lower
ovl: Add helper ovl_dentry_lowerdata() to get lower data dentry
ovl: Copy up meta inode data from lowest data inode
ovl: Modify ovl_lookup() and friends to lookup metacopy dentry
...
18 Jul, 2018
5 commits
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This reverts commit 4d0c5ba2ff79ef9f5188998b29fd28fcb05f3667.
We now get write access on both overlay and underlying layers so this patch
is no longer needed for correct operation.Signed-off-by: Miklos Szeredi
-
This reverts commit 495e642939114478a5237a7d91661ba93b76f15a.
No user of "flags" argument of d_real() remain.
Signed-off-by: Miklos Szeredi
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This reverts commit 7c6893e3c9abf6a9676e060a1e35e5caca673d57.
Overlayfs no longer relies on the vfs for checking writability of files.
Signed-off-by: Miklos Szeredi
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Let overlayfs do its thing when opening a file.
This enables stacking and fixes the corner case when a file is opened for
read, modified through a writable open, and data is read from the read-only
file. After this patch the read-only open will not return stale data even
in this case.Signed-off-by: Miklos Szeredi
Signed-off-by: Al Viro -
Stacking file operations in overlay will store an extra open file for each
overlay file opened.The overhead is just that of "struct file" which is about 256bytes, because
overlay already pins an extra dentry and inode when the file is open, which
add up to a much larger overhead.For fear of breaking working setups, don't start accounting the extra file.
Signed-off-by: Miklos Szeredi
12 Jul, 2018
11 commits
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open a file by given inode, faking ->f_path. Use with shitloads
of caution - at the very least you'd damn better make sure that
some dentry alias of that inode is pinned down by the path in
question. Again, this is no general-purpose interface and I hope
it will eventually go away. Right now overlayfs wants something
like that, but nothing else should.Any out-of-tree code with bright idea of using this one *will*
eventually get hurt, with zero notice and great delight on my part.
I refuse to use EXPORT_SYMBOL_GPL(), especially in situations when
it's really EXPORT_SYMBOL_DONT_USE_IT(), but don't take that export
as "you are welcome to use it".Signed-off-by: Al Viro
-
FMODE_OPENED can be used to distingusish "successful open" from the
"called finish_no_open(), do it yourself" cases. Since finish_no_open()
has been adjusted, no changes in the instances were actually needed.
The caller has been adjusted.Acked-by: Linus Torvalds
Signed-off-by: Al Viro -
'opened' argument of finish_open() is unused. Kill it.
Signed-off-by Al Viro
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... and don't bother with setting FILE_OPENED at all.
Acked-by: Linus Torvalds
Signed-off-by: Al Viro -
These checks are better off in do_dentry_open(); the reason we couldn't
put them there used to be that callers couldn't tell what kind of cleanup
would do_dentry_open() failure call for. Now that we have FMODE_OPENED,
cleanup is the same in all cases - it's simply fput(). So let's fold
that into do_dentry_open(), as Christoph's patch tried to.Acked-by: Linus Torvalds
Signed-off-by: Al Viro -
Just check FMODE_OPENED in __fput() and be done with that...
Acked-by: Linus Torvalds
Signed-off-by: Al Viro -
basically, "is that instance set up enough for regular fput(), or
do we want put_filp() for that one".NOTE: the only alloc_file() caller that could be followed by put_filp()
is in arch/ia64/kernel/perfmon.c, which is (Kconfig-level) broken.Acked-by: Linus Torvalds
Signed-off-by: Al Viro -
Acked-by: Linus Torvalds
Signed-off-by: Al Viro -
always equal to ->f_cred
Acked-by: Linus Torvalds
Signed-off-by: Al Viro -
... and have it set the f_flags-derived part of ->f_mode.
Signed-off-by: Al Viro
-
... and rename get_empty_filp() to alloc_empty_file().
dentry_open() gets creds as argument, but the only thing that sees those is
security_file_open() - file->f_cred still ends up with current_cred(). For
almost all callers it's the same thing, but there are several broken cases.Acked-by: Linus Torvalds
Signed-off-by: Al Viro
11 Jul, 2018
2 commits
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An ->open() instances really, really should not be doing that. There's
a lot of places e.g. around atomic_open() that could be confused by that,
so let's catch that early.Acked-by: Linus Torvalds
Signed-off-by: Al Viro -
it's exactly the same thing as
dentry_open(&file->f_path, file->f_flags, file->f_cred)... and rename it to file_clone_open(), while we are at it.
'filp' naming convention is bogus; sure, it's "file pointer",
but we generally don't do that kind of Hungarian notation.
Some of the instances have too many callers to touch, but this
one has only two, so let's sanitize it while we can...Acked-by: Linus Torvalds
Signed-off-by: Al Viro
04 Jun, 2018
1 commit
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This reverts commit cab64df194667dc5d9d786f0a895f647f5501c0d.
Having vfs_open() in some cases drop the reference to
struct file combined witherror = vfs_open(path, f, cred);
if (error) {
put_filp(f);
return ERR_PTR(error);
}
return f;is flat-out wrong. It used to be
error = vfs_open(path, f, cred);
if (!error) {
/* from now on we need fput() to dispose of f */
error = open_check_o_direct(f);
if (error) {
fput(f);
f = ERR_PTR(error);
}
} else {
put_filp(f);
f = ERR_PTR(error);
}and sure, having that open_check_o_direct() boilerplate gotten rid of is
nice, but not that way...Worse, another call chain (via finish_open()) is FUBAR now wrt
FILE_OPENED handling - in that case we get error returned, with file
already hit by fput() *AND* FILE_OPENED not set. Guess what happens in
path_openat(), when it hitsif (!(opened & FILE_OPENED)) {
BUG_ON(!error);
put_filp(file);
}The root cause of all that crap is that the callers of do_dentry_open()
have no way to tell which way did it fail; while that could be fixed up
(by passing something like int *opened to do_dentry_open() and have it
marked if we'd called ->open()), it's probably much too late in the
cycle to do so right now.Signed-off-by: Al Viro
Signed-off-by: Linus Torvalds
07 Apr, 2018
1 commit
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Pull misc vfs updates from Al Viro:
"Assorted stuff, including Christoph's I_DIRTY patches"* 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
fs: move I_DIRTY_INODE to fs.h
ubifs: fix bogus __mark_inode_dirty(I_DIRTY_SYNC | I_DIRTY_DATASYNC) call
ntfs: fix bogus __mark_inode_dirty(I_DIRTY_SYNC | I_DIRTY_DATASYNC) call
gfs2: fix bogus __mark_inode_dirty(I_DIRTY_SYNC | I_DIRTY_DATASYNC) calls
fs: fold open_check_o_direct into do_dentry_open
vfs: Replace stray non-ASCII homoglyph characters with their ASCII equivalents
vfs: make sure struct filename->iname is word-aligned
get rid of pointless includes of fs_struct.h
[poll] annotate SAA6588_CMD_POLL users
03 Apr, 2018
10 commits
-
Using the ksys_fallocate() wrapper allows us to get rid of in-kernel
calls to the sys_fallocate() syscall. The ksys_ prefix denotes that this
function is meant as a drop-in replacement for the syscall. In
particular, it uses the same calling convention as sys_fallocate().This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.netCc: Al Viro
Cc: Andrew Morton
Signed-off-by: Dominik Brodowski -
Using the ksys_truncate() wrapper allows us to get rid of in-kernel
calls to the sys_truncate() syscall. The ksys_ prefix denotes that this
function is meant as a drop-in replacement for the syscall. In
particular, it uses the same calling convention as sys_truncate().This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.netCc: Al Viro
Cc: Andrew Morton
Signed-off-by: Dominik Brodowski -
Using this wrapper allows us to avoid the in-kernel calls to the
sys_open() syscall. The ksys_ prefix denotes that this function is meant
as a drop-in replacement for the syscall. In particular, it uses the
same calling convention as sys_open().This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.netCc: Al Viro
Cc: Andrew Morton
Signed-off-by: Dominik Brodowski -
Using the ksys_close() wrapper allows us to get rid of in-kernel calls
to the sys_close() syscall. The ksys_ prefix denotes that this function
is meant as a drop-in replacement for the syscall. In particular, it
uses the same calling convention as sys_close(), with one subtle
difference:The few places which checked the return value did not care about the return
value re-writing in sys_close(), so simply use a wrapper around
__close_fd().This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.netCc: Al Viro
Cc: Andrew Morton
Signed-off-by: Dominik Brodowski -
Using the ksys_ftruncate() wrapper allows us to get rid of in-kernel
calls to the sys_ftruncate() syscall. The ksys_ prefix denotes that this
function is meant as a drop-in replacement for the syscall. In
particular, it uses the same calling convention as sys_ftruncate().This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.netCc: Al Viro
Cc: Andrew Morton
Signed-off-by: Dominik Brodowski -
Using the fs-interal do_fchownat() wrapper allows us to get rid of
fs-internal calls to the sys_fchownat() syscall.Introducing the ksys_fchown() helper and the ksys_{,}chown() wrappers
allows us to avoid the in-kernel calls to the sys_{,l,f}chown() syscalls.
The ksys_ prefix denotes that these functions are meant as a drop-in
replacement for the syscalls. In particular, they use the same calling
convention as sys_{,l,f}chown().This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.netCc: Al Viro
Cc: Andrew Morton
Signed-off-by: Dominik Brodowski -
Using the fs-internal do_faccessat() helper allows us to get rid of
fs-internal calls to the sys_faccessat() syscall.Introducing the ksys_access() wrapper allows us to avoid the in-kernel
calls to the sys_access() syscall. The ksys_ prefix denotes that this
function is meant as a drop-in replacement for the syscall. In
particular, it uses the same calling convention as sys_access().This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.netCc: Al Viro
Cc: Andrew Morton
Signed-off-by: Dominik Brodowski -
… in-kernel calls to syscall
Using the fs-internal do_fchmodat() helper allows us to get rid of
fs-internal calls to the sys_fchmodat() syscall.Introducing the ksys_fchmod() helper and the ksys_chmod() wrapper allows
us to avoid the in-kernel calls to the sys_fchmod() and sys_chmod()
syscalls. The ksys_ prefix denotes that these functions are meant as a
drop-in replacement for the syscalls. In particular, they use the same
calling convention as sys_fchmod() and sys_chmod().This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.netCc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net> -
Using this helper allows us to avoid the in-kernel calls to the sys_chdir()
syscall. The ksys_ prefix denotes that this function is meant as a drop-in
replacement for the syscall. In particular, it uses the same calling
convention as sys_chdir().This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.netCc: Al Viro
Cc: Andrew Morton
Signed-off-by: Dominik Brodowski -
Using this helper allows us to avoid the in-kernel calls to the
sys_chroot() syscall. The ksys_ prefix denotes that this function is
meant as a drop-in replacement for the syscall. In particular, it uses the
same calling convention as sys_chroot().In the near future, the fs-external callers of ksys_chroot() should be
converted to use kern_path()/set_fs_root() directly. Then ksys_chroot()
can be moved within sys_chroot() again.This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.netCc: Alexander Viro
Signed-off-by: Dominik Brodowski
28 Mar, 2018
1 commit
-
do_dentry_open is where we do the actual open of the file, so this is
where we should do our O_DIRECT sanity check to cover all potential
callers.Signed-off-by: Christoph Hellwig
Signed-off-by: Al Viro
05 Sep, 2017
2 commits
-
Problem with ioctl() is that it's a file operation, yet often used as an
inode operation (i.e. modify the inode despite the file being opened for
read-only).mnt_want_write_file() is used by filesystems in such cases to get write
access on an arbitrary open file.Since overlayfs lets filesystems do all file operations, including ioctl,
this can lead to mnt_want_write_file() returning OK for a lower file and
modification of that lower file.This patch prevents modification by checking if the file is from an
overlayfs lower layer and returning EPERM in that case.Need to introduce a mnt_want_write_file_path() variant that still does the
old thing for inode operations that can do the copy up + modification
correctly in such cases (fchown, fsetxattr, fremovexattr).This does not address the correctness of such ioctls on overlayfs (the
correct way would be to copy up and attempt to perform ioctl on upper
file).In theory this could be a regression. We very much hope that nobody is
relying on such a hack in any sane setup.While this patch meddles in VFS code, it has no effect on non-overlayfs
filesystems.Reported-by: "zhangyi (F)"
Signed-off-by: Miklos Szeredi -
Add a separate flags argument (in addition to the open flags) to control
the behavior of d_real().Signed-off-by: Miklos Szeredi
08 Jul, 2017
1 commit
-
Pull Writeback error handling updates from Jeff Layton:
"This pile represents the bulk of the writeback error handling fixes
that I have for this cycle. Some of the earlier patches in this pile
may look trivial but they are prerequisites for later patches in the
series.The aim of this set is to improve how we track and report writeback
errors to userland. Most applications that care about data integrity
will periodically call fsync/fdatasync/msync to ensure that their
writes have made it to the backing store.For a very long time, we have tracked writeback errors using two flags
in the address_space: AS_EIO and AS_ENOSPC. Those flags are set when a
writeback error occurs (via mapping_set_error) and are cleared as a
side-effect of filemap_check_errors (as you noted yesterday). This
model really sucks for userland.Only the first task to call fsync (or msync or fdatasync) will see the
error. Any subsequent task calling fsync on a file will get back 0
(unless another writeback error occurs in the interim). If I have
several tasks writing to a file and calling fsync to ensure that their
writes got stored, then I need to have them coordinate with one
another. That's difficult enough, but in a world of containerized
setups that coordination may even not be possible.But wait...it gets worse!
The calls to filemap_check_errors can be buried pretty far down in the
call stack, and there are internal callers of filemap_write_and_wait
and the like that also end up clearing those errors. Many of those
callers ignore the error return from that function or return it to
userland at nonsensical times (e.g. truncate() or stat()). If I get
back -EIO on a truncate, there is no reason to think that it was
because some previous writeback failed, and a subsequent fsync() will
(incorrectly) return 0.This pile aims to do three things:
1) ensure that when a writeback error occurs that that error will be
reported to userland on a subsequent fsync/fdatasync/msync call,
regardless of what internal callers are doing2) report writeback errors on all file descriptions that were open at
the time that the error occurred. This is a user-visible change,
but I think most applications are written to assume this behavior
anyway. Those that aren't are unlikely to be hurt by it.3) document what filesystems should do when there is a writeback
error. Today, there is very little consistency between them, and a
lot of cargo-cult copying. We need to make it very clear what
filesystems should do in this situation.To achieve this, the set adds a new data type (errseq_t) and then
builds new writeback error tracking infrastructure around that. Once
all of that is in place, we change the filesystems to use the new
infrastructure for reporting wb errors to userland.Note that this is just the initial foray into cleaning up this mess.
There is a lot of work remaining here:1) convert the rest of the filesystems in a similar fashion. Once the
initial set is in, then I think most other fs' will be fairly
simple to convert. Hopefully most of those can in via individual
filesystem trees.2) convert internal waiters on writeback to use errseq_t for
detecting errors instead of relying on the AS_* flags. I have some
draft patches for this for ext4, but they are not quite ready for
prime time yet.This was a discussion topic this year at LSF/MM too. If you're
interested in the gory details, LWN has some good articles about this:https://lwn.net/Articles/718734/
https://lwn.net/Articles/724307/"* tag 'for-linus-v4.13-2' of git://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux:
btrfs: minimal conversion to errseq_t writeback error reporting on fsync
xfs: minimal conversion to errseq_t writeback error reporting
ext4: use errseq_t based error handling for reporting data writeback errors
fs: convert __generic_file_fsync to use errseq_t based reporting
block: convert to errseq_t based writeback error tracking
dax: set errors in mapping when writeback fails
Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors
mm: set both AS_EIO/AS_ENOSPC and errseq_t in mapping_set_error
fs: new infrastructure for writeback error handling and reporting
lib: add errseq_t type and infrastructure for handling it
mm: don't TestClearPageError in __filemap_fdatawait_range
mm: clear AS_EIO/AS_ENOSPC when writeback initiation fails
jbd2: don't clear and reset errors after waiting on writeback
buffer: set errors in mapping at the time that the error occurs
fs: check for writeback errors after syncing out buffers in generic_file_fsync
buffer: use mapping_set_error instead of setting the flag
mm: fix mapping_set_error call in me_pagecache_dirty
06 Jul, 2017
1 commit
-
Most filesystems currently use mapping_set_error and
filemap_check_errors for setting and reporting/clearing writeback errors
at the mapping level. filemap_check_errors is indirectly called from
most of the filemap_fdatawait_* functions and from
filemap_write_and_wait*. These functions are called from all sorts of
contexts to wait on writeback to finish -- e.g. mostly in fsync, but
also in truncate calls, getattr, etc.The non-fsync callers are problematic. We should be reporting writeback
errors during fsync, but many places spread over the tree clear out
errors before they can be properly reported, or report errors at
nonsensical times.If I get -EIO on a stat() call, there is no reason for me to assume that
it is because some previous writeback failed. The fact that it also
clears out the error such that a subsequent fsync returns 0 is a bug,
and a nasty one since that's potentially silent data corruption.This patch adds a small bit of new infrastructure for setting and
reporting errors during address_space writeback. While the above was my
original impetus for adding this, I think it's also the case that
current fsync semantics are just problematic for userland. Most
applications that call fsync do so to ensure that the data they wrote
has hit the backing store.In the case where there are multiple writers to the file at the same
time, this is really hard to determine. The first one to call fsync will
see any stored error, and the rest get back 0. The processes with open
fds may not be associated with one another in any way. They could even
be in different containers, so ensuring coordination between all fsync
callers is not really an option.One way to remedy this would be to track what file descriptor was used
to dirty the file, but that's rather cumbersome and would likely be
slow. However, there is a simpler way to improve the semantics here
without incurring too much overhead.This set adds an errseq_t to struct address_space, and a corresponding
one is added to struct file. Writeback errors are recorded in the
mapping's errseq_t, and the one in struct file is used as the "since"
value.This changes the semantics of the Linux fsync implementation such that
applications can now use it to determine whether there were any
writeback errors since fsync(fd) was last called (or since the file was
opened in the case of fsync having never been called).Note that those writeback errors may have occurred when writing data
that was dirtied via an entirely different fd, but that's the case now
with the current mapping_set_error/filemap_check_error infrastructure.
This will at least prevent you from getting a false report of success.The new behavior is still consistent with the POSIX spec, and is more
reliable for application developers. This patch just adds some basic
infrastructure for doing this, and ensures that the f_wb_err "cursor"
is properly set when a file is opened. Later patches will change the
existing code to use this new infrastructure for reporting errors at
fsync time.Signed-off-by: Jeff Layton
Reviewed-by: Jan Kara
28 Jun, 2017
1 commit
-
Define a set of write life time hints:
RWH_WRITE_LIFE_NOT_SET No hint information set
RWH_WRITE_LIFE_NONE No hints about write life time
RWH_WRITE_LIFE_SHORT Data written has a short life time
RWH_WRITE_LIFE_MEDIUM Data written has a medium life time
RWH_WRITE_LIFE_LONG Data written has a long life time
RWH_WRITE_LIFE_EXTREME Data written has an extremely long life timeThe intent is for these values to be relative to each other, no
absolute meaning should be attached to these flag names.Add an fcntl interface for querying these flags, and also for
setting them as well:F_GET_RW_HINT Returns the read/write hint set on the
underlying inode.F_SET_RW_HINT Set one of the above write hints on the
underlying inode.F_GET_FILE_RW_HINT Returns the read/write hint set on the
file descriptor.F_SET_FILE_RW_HINT Set one of the above write hints on the
file descriptor.The user passes in a 64-bit pointer to get/set these values, and
the interface returns 0/-1 on success/error.Sample program testing/implementing basic setting/getting of write
hints is below.Add support for storing the write life time hint in the inode flags
and in struct file as well, and pass them to the kiocb flags. If
both a file and its corresponding inode has a write hint, then we
use the one in the file, if available. The file hint can be used
for sync/direct IO, for buffered writeback only the inode hint
is available.This is in preparation for utilizing these hints in the block layer,
to guide on-media data placement./*
* writehint.c: get or set an inode write hint
*/
#include
#include
#include
#include
#include
#include#ifndef F_GET_RW_HINT
#define F_LINUX_SPECIFIC_BASE 1024
#define F_GET_RW_HINT (F_LINUX_SPECIFIC_BASE + 11)
#define F_SET_RW_HINT (F_LINUX_SPECIFIC_BASE + 12)
#endifstatic char *str[] = { "RWF_WRITE_LIFE_NOT_SET", "RWH_WRITE_LIFE_NONE",
"RWH_WRITE_LIFE_SHORT", "RWH_WRITE_LIFE_MEDIUM",
"RWH_WRITE_LIFE_LONG", "RWH_WRITE_LIFE_EXTREME" };int main(int argc, char *argv[])
{
uint64_t hint;
int fd, ret;if (argc < 2) {
fprintf(stderr, "%s: file \n", argv[0]);
return 1;
}fd = open(argv[1], O_RDONLY);
if (fd < 0) {
perror("open");
return 2;
}if (argc > 2) {
hint = atoi(argv[2]);
ret = fcntl(fd, F_SET_RW_HINT, &hint);
if (ret < 0) {
perror("fcntl: F_SET_RW_HINT");
return 4;
}
}ret = fcntl(fd, F_GET_RW_HINT, &hint);
if (ret < 0) {
perror("fcntl: F_GET_RW_HINT");
return 3;
}printf("%s: hint %s\n", argv[1], str[hint]);
close(fd);
return 0;
}Reviewed-by: Martin K. Petersen
Signed-off-by: Jens Axboe
