16 Jan, 2011
1 commit
-
…linus' and 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
rcu: avoid pointless blocked-task warnings
rcu: demote SRCU_SYNCHRONIZE_DELAY from kernel-parameter status
rtmutex: Fix comment about why new_owner can be NULL in wake_futex_pi()* 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
x86, olpc: Add missing Kconfig dependencies
x86, mrst: Set correct APB timer IRQ affinity for secondary cpu
x86: tsc: Fix calibration refinement conditionals to avoid divide by zero
x86, ia64, acpi: Clean up x86-ism in drivers/acpi/numa.c* 'timers-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
timekeeping: Make local variables static
time: Rename misnamed minsec argument of clocks_calc_mult_shift()* 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
tracing: Remove syscall_exit_fields
tracing: Only process module tracepoints once
perf record: Add "nodelay" mode, disabled by default
perf sched: Fix list of events, dropping unsupported ':r' modifier
Revert "perf tools: Emit clearer message for sys_perf_event_open ENOENT return"
perf top: Fix annotate segv
perf evsel: Fix order of event list deletion
14 Jan, 2011
1 commit
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Futex code is smarter than most other gup_fast O_DIRECT code and knows
about the compound internals. However now doing a put_page(head_page)
will not release the pin on the tail page taken by gup-fast, leading to
all sort of refcounting bugchecks. Getting a stable head_page is a little
tricky.page_head = page is there because if this is not a tail page it's also the
page_head. Only in case this is a tail page, compound_head is called,
otherwise it's guaranteed unnecessary. And if it's a tail page
compound_head has to run atomically inside irq disabled section
__get_user_pages_fast before returning. Otherwise ->first_page won't be a
stable pointer.Disableing irq before __get_user_page_fast and releasing irq after running
compound_head is needed because if __get_user_page_fast returns == 1, it
means the huge pmd is established and cannot go away from under us.
pmdp_splitting_flush_notify in __split_huge_page_splitting will have to
wait for local_irq_enable before the IPI delivery can return. This means
__split_huge_page_refcount can't be running from under us, and in turn
when we run compound_head(page) we're not reading a dangling pointer from
tailpage->first_page. Then after we get to stable head page, we are
always safe to call compound_lock and after taking the compound lock on
head page we can finally re-check if the page returned by gup-fast is
still a tail page. in which case we're set and we didn't need to split
the hugepage in order to take a futex on it.Signed-off-by: Andrea Arcangeli
Acked-by: Mel Gorman
Acked-by: Rik van Riel
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
11 Jan, 2011
1 commit
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The comment about why rt_mutex_next_owner() can return NULL in
wake_futex_pi() is not the normal case.Tracing the cause of why this occurs is more likely that waiter
simply timedout. But because it originally caused contention with
the futex, the owner will go into the kernel when it unlocks
the lock. Then it will hit this code path and
rt_mutex_next_owner() will return NULL.Cc: Thomas Gleixner
Signed-off-by: Steven Rostedt
Signed-off-by: Ingo Molnar
10 Nov, 2010
4 commits
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The futex_q struct has grown considerably over the last couple years. I
believe it now merits a static initializer to avoid uninitialized data
errors (having spent more time than I care to admit debugging an uninitialized
q.bitset in an experimental new op code).With the key initializer built in, several of the FUTEX_KEY_INIT calls can
be removed.V2: use a static variable instead of an init macro.
use a C99 initializer and don't rely on variable ordering in the struct.
V3: make futex_q_init constSigned-off-by: Darren Hart
Cc: Peter Zijlstra
Cc: Eric Dumazet
Cc: John Kacur
Cc: Ingo Molnar
LKML-Reference:
Signed-off-by: Thomas Gleixner -
In the early days we passed the mmap sem around. That became the
"int fshared" with the fast gup improvements. Then we added
"int clockrt" in places. This patch unifies these options as "flags".[ tglx: Split out the stale fshared cleanup ]
Signed-off-by: Darren Hart
Cc: Peter Zijlstra
Cc: Eric Dumazet
Cc: John Kacur
Cc: Ingo Molnar
LKML-Reference:
Signed-off-by: Thomas Gleixner -
The fast GUP changes stopped using the fshared flag in
put_futex_keys(), but we kept the interface the same.Cleanup all stale users.
This patch is split out from Darren Harts combo patch which also
combines various flags. This way the changes are clearly separated.Signed-off-by: Thomas Gleixner
Cc: Darren Hart
LKML-Reference: -
Since commit 1dcc41bb (futex: Change 3rd arg of fetch_robust_entry()
to unsigned int*) some gcc versions decided to emit the following
warning:kernel/futex.c: In function ‘exit_robust_list’:
kernel/futex.c:2492: warning: ‘next_pi’ may be used uninitialized in this functionThe commit did not introduce the warning as gcc should have warned
before that commit as well. It's just gcc being silly.The code path really can't result in next_pi being unitialized (or
should not), but let's keep the build clean. Annotate next_pi as an
uninitialized_var.[ tglx: Addressed the same issue in futex_compat.c and massaged the
changelog ]Signed-off-by: Darren Hart
Tested-by: Matt Fleming
Tested-by: Uwe Kleine-König
Cc: Peter Zijlstra
Cc: Eric Dumazet
Cc: John Kacur
Cc: Ingo Molnar
LKML-Reference:
Signed-off-by: Thomas Gleixner
26 Oct, 2010
1 commit
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Clones an existing reference to inode; caller must already hold one.
Signed-off-by: Al Viro
22 Oct, 2010
1 commit
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* 'futexes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
futex: Fix kernel-doc notation & typos
futex: Add lock context annotations
futex: Mark restart_block.futex.uaddr[2] __user
futex: Change 3rd arg of fetch_robust_entry() to unsigned int*
19 Oct, 2010
1 commit
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futex_wait() is leaking key references due to futex_wait_setup()
acquiring an additional reference via the queue_lock() routine. The
nested key ref-counting has been masking bugs and complicating code
analysis. queue_lock() is only called with a previously ref-counted
key, so remove the additional ref-counting from the queue_(un)lock()
functions.Also futex_wait_requeue_pi() drops one key reference too many in
unqueue_me_pi(). Remove the key reference handling from
unqueue_me_pi(). This was paired with a queue_lock() in
futex_lock_pi(), so the count remains unchanged.Document remaining nested key ref-counting sites.
Signed-off-by: Darren Hart
Reported-and-tested-by: Matthieu Fertré
Reported-by: Louis Rilling
Cc: Peter Zijlstra
Cc: Eric Dumazet
Cc: John Kacur
Cc: Rusty Russell
LKML-Reference:
Signed-off-by: Thomas Gleixner
Cc: stable@kernel.org
14 Oct, 2010
1 commit
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Convert futex_requeue() function parameters to use @name
kernel-doc notation and add @fshared & @cmpval to prevent
kernel-doc warnings.Add @list to struct futex_q.
Fix a few typos.
Signed-off-by: Randy Dunlap
Acked-by: Rusty Russell
LKML-Reference:
Signed-off-by: Ingo Molnar
18 Sep, 2010
3 commits
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queue_lock/unlock/me() and unqueue_me_pi() grab/release spinlocks
but are missing proper annotations. Add them.Signed-off-by: Namhyung Kim
Cc: Peter Zijlstra
Cc: Darren Hart
LKML-Reference:
Signed-off-by: Thomas Gleixner -
@uaddr and @uaddr2 fields in restart_block.futex are user
pointers. Add __user and remove unnecessary casts.Signed-off-by: Namhyung Kim
Cc: Peter Zijlstra
Cc: Darren Hart
LKML-Reference:
Signed-off-by: Thomas Gleixner -
Sparse complains:
kernel/futex.c:2495:59: warning: incorrect type in argument 3 (different signedness)Make 3rd argument of fetch_robust_entry() 'unsigned int'.
Signed-off-by: Namhyung Kim
Cc: Peter Zijlstra
Cc: Darren Hart
LKML-Reference:
Signed-off-by: Thomas Gleixner
01 Jul, 2010
1 commit
-
futex_find_get_task is currently used (through lookup_pi_state) from two
contexts, futex_requeue and futex_lock_pi_atomic. None of the paths
looks it needs the credentials check, though. Different (e)uids
shouldn't matter at all because the only thing that is important for
shared futex is the accessibility of the shared memory.The credentail check results in glibc assert failure or process hang (if
glibc is compiled without assert support) for shared robust pthread
mutex with priority inheritance if a process tries to lock already held
lock owned by a process with a different euid:pthread_mutex_lock.c:312: __pthread_mutex_lock_full: Assertion `(-(e)) != 3 || !robust' failed.
The problem is that futex_lock_pi_atomic which is called when we try to
lock already held lock checks the current holder (tid is stored in the
futex value) to get the PI state. It uses lookup_pi_state which in turn
gets task struct from futex_find_get_task. ESRCH is returned either
when the task is not found or if credentials check fails.futex_lock_pi_atomic simply returns if it gets ESRCH. glibc code,
however, doesn't expect that robust lock returns with ESRCH because it
should get either success or owner died.Signed-off-by: Michal Hocko
Acked-by: Darren Hart
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Nick Piggin
Cc: Alexey Kuznetsov
Cc: Peter Zijlstra
Signed-off-by: Linus Torvalds
03 Feb, 2010
3 commits
-
The WARN_ON in lookup_pi_state which complains about a mismatch
between pi_state->owner->pid and the pid which we retrieved from the
user space futex is completely bogus.The code just emits the warning and then continues despite the fact
that it detected an inconsistent state of the futex. A conveniant way
for user space to spam the syslog.Replace the WARN_ON by a consistency check. If the values do not match
return -EINVAL and let user space deal with the mess it created.This also fixes the missing task_pid_vnr() when we compare the
pi_state->owner pid with the futex value.Reported-by: Jermome Marchand
Signed-off-by: Thomas Gleixner
Acked-by: Darren Hart
Acked-by: Peter Zijlstra
Cc: -
If the owner of a PI futex dies we fix up the pi_state and set
pi_state->owner to NULL. When a malicious or just sloppy programmed
user space application sets the futex value to 0 e.g. by calling
pthread_mutex_init(), then the futex can be acquired again. A new
waiter manages to enqueue itself on the pi_state w/o damage, but on
unlock the kernel dereferences pi_state->owner and oopses.Prevent this by checking pi_state->owner in the unlock path. If
pi_state->owner is not current we know that user space manipulated the
futex value. Ignore the mess and return -EINVAL.This catches the above case and also the case where a task hijacks the
futex by setting the tid value and then tries to unlock it.Reported-by: Jermome Marchand
Signed-off-by: Thomas Gleixner
Acked-by: Darren Hart
Acked-by: Peter Zijlstra
Cc: -
This fixes a futex key reference count bug in futex_lock_pi(),
where a key's reference count is incremented twice but decremented
only once, causing the backing object to not be released.If the futex is created in a temporary file in an ext3 file system,
this bug causes the file's inode to become an "undead" orphan,
which causes an oops from a BUG_ON() in ext3_put_super() when the
file system is unmounted. glibc's test suite is known to trigger this,
see .The bug is a regression from 2.6.28-git3, namely Peter Zijlstra's
38d47c1b7075bd7ec3881141bb3629da58f88dab "[PATCH] futex: rely on
get_user_pages() for shared futexes". That commit made get_futex_key()
also increment the reference count of the futex key, and updated its
callers to decrement the key's reference count before returning.
Unfortunately the normal exit path in futex_lock_pi() wasn't corrected:
the reference count is incremented by get_futex_key() and queue_lock(),
but the normal exit path only decrements once, via unqueue_me_pi().
The fix is to put_futex_key() after unqueue_me_pi(), since 2.6.31
this is easily done by 'goto out_put_key' rather than 'goto out'.Signed-off-by: Mikael Pettersson
Acked-by: Peter Zijlstra
Acked-by: Darren Hart
Signed-off-by: Thomas Gleixner
Cc:
13 Jan, 2010
1 commit
-
Currently, futexes have two problem:
A) The current futex code doesn't handle private file mappings properly.
get_futex_key() uses PageAnon() to distinguish file and
anon, which can cause the following bad scenario:1) thread-A call futex(private-mapping, FUTEX_WAIT), it
sleeps on file mapping object.
2) thread-B writes a variable and it makes it cow.
3) thread-B calls futex(private-mapping, FUTEX_WAKE), it
wakes up blocked thread on the anonymous page. (but it's nothing)B) Current futex code doesn't handle zero page properly.
Read mode get_user_pages() can return zero page, but current
futex code doesn't handle it at all. Then, zero page makes
infinite loop internally.The solution is to use write mode get_user_page() always for
page lookup. It prevents the lookup of both file page of private
mappings and zero page.Performance concerns:
Probaly very little, because glibc always initialize variables
for futex before to call futex(). It means glibc users never see
the overhead of this patch.Compatibility concerns:
This patch has few compatibility issues. After this patch,
FUTEX_WAIT require writable access to futex variables (read-only
mappings makes EFAULT). But practically it's not a problem,
glibc always initalizes variables for futexes explicitly - nobody
uses read-only mappings.Reported-by: Hugh Dickins
Signed-off-by: KOSAKI Motohiro
Acked-by: Peter Zijlstra
Acked-by: Darren Hart
Cc:
Cc: Linus Torvalds
Cc: KAMEZAWA Hiroyuki
Cc: Nick Piggin
Cc: Ulrich Drepper
LKML-Reference:
Signed-off-by: Ingo Molnar
15 Dec, 2009
3 commits
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Convert locks which cannot be sleeping locks in preempt-rt to
raw_spinlocks.Signed-off-by: Thomas Gleixner
Acked-by: Peter Zijlstra
Acked-by: Ingo Molnar -
Convert locks which cannot be sleeping locks in preempt-rt to
raw_spinlocks.Signed-off-by: Thomas Gleixner
Acked-by: Peter Zijlstra
Acked-by: Ingo Molnar -
plists are used with spinlocks and raw_spinlocks. Change the plist
debugging to handle both types.Signed-off-by: Thomas Gleixner
Acked-by: Peter Zijlstra
Acked-by: Ingo Molnar
08 Dec, 2009
1 commit
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get_user_pages() must be called with mmap_sem held.
Signed-off-by: Andi Kleen
Cc: stable@kernel.org
Cc: Andrew Morton
Cc: Nick Piggin
Cc: Darren Hart
Cc: Peter Zijlstra
LKML-Reference:
Signed-off-by: Thomas Gleixner
29 Oct, 2009
1 commit
-
The requeue_pi path doesn't use unqueue_me() (and the racy lock_ptr ==
NULL test) nor does it use the wake_list of futex_wake() which where
the reason for commit 41890f2 (futex: Handle spurious wake up)See debugging discussing on LKML Message-ID:
The changes in this fix to the wait_requeue_pi path were considered to
be a likely unecessary, but harmless safety net. But it turns out that
due to the fact that for unknown $@#!*( reasons EWOULDBLOCK is defined
as EAGAIN we built an endless loop in the code path which returns
correctly EWOULDBLOCK.Spurious wakeups in wait_requeue_pi code path are unlikely so we do
the easy solution and return EWOULDBLOCK^WEAGAIN to user space and let
it deal with the spurious wakeup.Cc: Darren Hart
Cc: Peter Zijlstra
Cc: Eric Dumazet
Cc: John Stultz
Cc: Dinakar Guniguntala
LKML-Reference:
Cc: stable@kernel.org
Signed-off-by: Thomas Gleixner
16 Oct, 2009
1 commit
-
When requeuing tasks from one futex to another, the reference held
by the requeued task to the original futex location needs to be
dropped eventually.Dropping the reference may ultimately lead to a call to
"iput_final" and subsequently call into filesystem- specific code -
which may be non-atomic.It is therefore safer to defer this drop operation until after the
futex_hash_bucket spinlock has been dropped.Originally-From: Helge Bahmann
Signed-off-by: Darren Hart
Cc:
Cc: Peter Zijlstra
Cc: Eric Dumazet
Cc: Dinakar Guniguntala
Cc: John Stultz
Cc: Sven-Thorsten Dietrich
Cc: John Kacur
LKML-Reference:
Signed-off-by: Ingo Molnar
15 Oct, 2009
1 commit
-
If userspace tries to perform a requeue_pi on a non-requeue_pi waiter,
it will find the futex_q->requeue_pi_key to be NULL and OOPS.Check for NULL in match_futex() instead of doing explicit NULL pointer
checks on all call sites. While match_futex(NULL, NULL) returning
false is a little odd, it's still correct as we expect valid key
references.Signed-off-by: Darren Hart
Cc: Peter Zijlstra
Cc: Ingo Molnar
CC: Eric Dumazet
CC: Dinakar Guniguntala
CC: John Stultz
Cc: stable@kernel.org
LKML-Reference:
Signed-off-by: Thomas Gleixner
14 Oct, 2009
1 commit
-
The futex code does not handle spurious wake up in futex_wait and
futex_wait_requeue_pi.The code assumes that any wake up which was not caused by futex_wake /
requeue or by a timeout was caused by a signal wake up and returns one
of the syscall restart error codes.In case of a spurious wake up the signal delivery code which deals
with the restart error codes is not invoked and we return that error
code to user space. That causes applications which actually check the
return codes to fail. Blaise reported that on preempt-rt a python test
program run into a exception trap. -rt exposed that due to a built in
spurious wake up accelerator :)Solve this by checking signal_pending(current) in the wake up path and
handle the spurious wake up case w/o returning to user space.Reported-by: Blaise Gassend
Debugged-by: Darren Hart
Signed-off-by: Thomas Gleixner
Cc: Peter Zijlstra
Cc: stable@kernel.org
LKML-Reference:
09 Oct, 2009
1 commit
-
…/git/tip/linux-2.6-tip
* 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
futex: fix requeue_pi key imbalance
futex: Fix typo in FUTEX_WAIT/WAKE_BITSET_PRIVATE definitions
rcu: Place root rcu_node structure in separate lockdep class
rcu: Make hot-unplugged CPU relinquish its own RCU callbacks
rcu: Move rcu_barrier() to rcutree
futex: Move exit_pi_state() call to release_mm()
futex: Nullify robust lists after cleanup
futex: Fix locking imbalance
panic: Fix panic message visibility by calling bust_spinlocks(0) before dying
rcu: Replace the rcu_barrier enum with pointer to call_rcu*() function
rcu: Clean up code based on review feedback from Josh Triplett, part 4
rcu: Clean up code based on review feedback from Josh Triplett, part 3
rcu: Fix rcu_lock_map build failure on CONFIG_PROVE_LOCKING=y
rcu: Clean up code to address Ingo's checkpatch feedback
rcu: Clean up code based on review feedback from Josh Triplett, part 2
rcu: Clean up code based on review feedback from Josh Triplett
08 Oct, 2009
1 commit
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If futex_wait_requeue_pi() wakes prior to requeue, we drop the
reference to the source futex_key twice, once in
handle_early_requeue_pi_wakeup() and once on our way out.Remove the drop from the handle_early_requeue_pi_wakeup() and keep
the get/drops together in futex_wait_requeue_pi().Reported-by: Helge Bahmann
Signed-off-by: Darren Hart
Cc: Helge Bahmann
Cc: Peter Zijlstra
Cc: Eric Dumazet
Cc: Dinakar Guniguntala
Cc: John Stultz
Cc: stable-2.6.31
LKML-Reference:
Signed-off-by: Thomas Gleixner
06 Oct, 2009
1 commit
-
Rich reported a lock imbalance in the futex code:
http://bugzilla.kernel.org/show_bug.cgi?id=14288
It's caused by the displacement of the retry_private label in
futex_wake_op(). The code unlocks the hash bucket locks in the
error handling path and retries without locking them again which
makes the next unlock fail.Move retry_private so we lock the hash bucket locks when we retry.
Reported-by: Rich Ercolany
Signed-off-by: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Darren Hart
Cc: stable-2.6.31
LKML-Reference:
Signed-off-by: Ingo Molnar
25 Sep, 2009
1 commit
-
The memory barrier semantics of futex_wait_queue_me() are
non-obvious. Add some commentary to try and clarify it.Signed-off-by: Darren Hart
Cc: Peter Zijlstra
Cc: Eric Dumazet
Cc: Dinakar Guniguntala
Cc: John Stultz
LKML-Reference:
Signed-off-by: Ingo Molnar
22 Sep, 2009
5 commits
-
PI futexes do not use the same plist_node_empty() test for wakeup.
It was possible for the waiter (in futex_wait_requeue_pi()) to set
TASK_INTERRUPTIBLE after the waker assigned the rtmutex to the
waiter. The waiter would then note the plist was not empty and call
schedule(). The task would not be found by any subsequeuent futex
wakeups, resulting in a userspace hang.By moving the setting of TASK_INTERRUPTIBLE to before the call to
queue_me(), the race with the waker is eliminated. Since we no
longer call get_user() from within queue_me(), there is no need to
delay the setting of TASK_INTERRUPTIBLE until after the call to
queue_me().The FUTEX_LOCK_PI operation is not affected as futex_lock_pi()
relies entirely on the rtmutex code to handle schedule() and
wakeup. The requeue PI code is affected because the waiter starts
as a non-PI waiter and is woken on a PI futex.Remove the crusty old comment about holding spinlocks() across
get_user() as we no longer do that. Correct the locking statement
with a description of why the test is performed.Signed-off-by: Darren Hart
Acked-by: Peter Zijlstra
Cc: Steven Rostedt
Cc: Eric Dumazet
Cc: Dinakar Guniguntala
Cc: John Stultz
LKML-Reference:
Signed-off-by: Ingo Molnar -
Use kernel-doc format to describe struct futex_q.
Correct the wakeup definition to eliminate the statement about
waking the waiter between the plist_del() and the q->lock_ptr = 0.Note in the comment that PI futexes have a different definition of
the woken state.Signed-off-by: Darren Hart
Acked-by: Peter Zijlstra
Cc: Steven Rostedt
Cc: Eric Dumazet
Cc: Dinakar Guniguntala
Cc: John Stultz
LKML-Reference:
Signed-off-by: Ingo Molnar -
Make the existing function kernel-doc consistent throughout
futex.c, following Documentation/kernel-doc-nano-howto.txt as
closely as possible.When unsure, at least be consistent within futex.c.
Signed-off-by: Darren Hart
Acked-by: Peter Zijlstra
Cc: Steven Rostedt
Cc: Eric Dumazet
Cc: Dinakar Guniguntala
Cc: John Stultz
LKML-Reference:
Signed-off-by: Ingo Molnar -
The queue_me/unqueue_me commentary is oddly placed and out of date.
Clean it up and correct the inaccurate bits.Signed-off-by: Darren Hart
Acked-by: Peter Zijlstra
Cc: Steven Rostedt
Cc: Eric Dumazet
Cc: Dinakar Guniguntala
Cc: John Stultz
LKML-Reference:
Signed-off-by: Ingo Molnar -
Correct various typos and formatting inconsistencies in the
commentary of futex_wait_requeue_pi().Signed-off-by: Darren Hart
Acked-by: Peter Zijlstra
Cc: Steven Rostedt
Cc: Eric Dumazet
Cc: Dinakar Guniguntala
Cc: John Stultz
LKML-Reference:
Signed-off-by: Ingo Molnar
12 Sep, 2009
1 commit
-
…el/git/tip/linux-2.6-tip
* 'core-futexes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
futex: Detect mismatched requeue targets
futex: Correct futex_wait_requeue_pi() commentary
16 Aug, 2009
1 commit
-
There is currently no check to ensure that userspace uses the same
futex requeue target (uaddr2) in futex_requeue() that the waiter used
in futex_wait_requeue_pi(). A mismatch here could very unexpected
results as the waiter assumes it either wakes on uaddr1 or uaddr2. We
could detect this on wakeup in the waiter, but the cleanup is more
intense after the improper requeue has occured.This patch stores the waiter's expected requeue target in a new
requeue_pi_key pointer in the futex_q which futex_requeue() checks
prior to attempting to do a proxy lock acquistion or a requeue when
requeue_pi=1. If they don't match, return -EINVAL from futex_requeue,
aborting the requeue of any remaining waiters.Signed-off-by: Darren Hart
Cc: Peter Zijlstra
Cc: Eric Dumazet
Cc: John Kacur
Cc: Dinakar Guniguntala
Cc: John Stultz
LKML-Reference:
Signed-off-by: Thomas Gleixner
11 Aug, 2009
1 commit
-
If futex_requeue(requeue_pi=1) finds a futex_q that was created by a call
other the futex_wait_requeue_pi(), the q.rt_waiter may be null. If so,
this will result in an oops from the following call graph:futex_requeue()
rt_mutex_start_proxy_lock()
task_blocks_on_rt_mutex()
waiter->task dereference
OOPSWe currently WARN_ON() if this is detected, clearly this is inadequate.
If we detect a mispairing in futex_requeue(), bail out, seding -EINVAL to
user-space.V2: Fix parenthesis warnings.
Signed-off-by: Darren Hart
Acked-by: Peter Zijlstra
Cc: Steven Rostedt
Cc: John Kacur
Cc: Eric Dumazet
Cc: Dinakar Guniguntala
Cc: John Stultz
LKML-Reference:
Signed-off-by: Ingo Molnar
10 Aug, 2009
1 commit
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futex_requeue() can acquire the lock on behalf of a waiter
early on or during the requeue loop if it is uncontended or in
the event of a lock steal or owner died. On wakeup, the waiter
(in futex_wait_requeue_pi()) cleans up the pi_state owner using
the lock_ptr to protect against concurrent access to the
pi_state. The pi_state is hung off futex_q's on the requeue
target futex hash bucket so the lock_ptr needs to be updated
accordingly.The problem manifested by triggering the WARN_ON in
lookup_pi_state() about the pid != pi_state->owner->pid. With
this patch, the pi_state is properly guarded against concurrent
access via the requeue target hb lock.The astute reviewer may notice that there is a window of time
between when futex_requeue() unlocks the hb locks and when
futex_wait_requeue_pi() will acquire hb2->lock. During this
time the pi_state and uval are not in sync with the underlying
rtmutex owner (but the uval does indicate there are waiters, so
no atomic changes will occur in userspace). However, this is
not a problem. Should a contending thread enter
lookup_pi_state() and acquire hb2->lock before the ownership is
fixed up, it will find the pi_state hung off a waiter's
(possibly the pending owner's) futex_q and block on the
rtmutex. Once futex_wait_requeue_pi() fixes up the owner, it
will also move the pi_state from the old owner's
task->pi_state_list to its own.v3: Fix plist lock name for application to mainline (rather
than -rt) Compile tested against tip/v2.6.31-rc5.Signed-off-by: Darren Hart
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Eric Dumazet
Cc: Dinakar Guniguntala
Cc: John Stultz
LKML-Reference:
Signed-off-by: Ingo Molnar