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Commit ce3b642d42f36406112ab474c03d81c5941d9398

Authored by Jeff Dike
Committed by Linus Torvalds
1 parent 0a765329ed

uml: work around host tcsetattr bug 

Under the conditions that UML uses it, tcgetattr is guaranteed to return
-EINTR when the console is attached to /dev/ptmx, making generic_console_write
hang because it loops, calling tcgetattr until it succeeds.  This is a host
bug - see http://marc.info/?l=linux-kernel&m=119618990807182&w=2 for the
details.

This patch works around it by blocking SIGIO while the terminal attributes are
being fiddled.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Showing 1 changed file with 10 additions and 1 deletions Side-by-side Diff

arch/um/drivers/chan_user.c
Diff comments   View file @ ce3b642
... ... @@ -74,10 +74,16 @@
74 74  
75 75 int generic_console_write(int fd, const char *buf, int n)
76 76 {
  77 + sigset_t old, no_sigio;
77 78 struct termios save, new;
78 79 int err;
79 80  
80 81 if (isatty(fd)) {
  82 + sigemptyset(&no_sigio);
  83 + sigaddset(&no_sigio, SIGIO);
  84 + if (sigprocmask(SIG_BLOCK, &no_sigio, &old))
  85 + goto error;
  86 +
81 87 CATCH_EINTR(err = tcgetattr(fd, &save));
82 88 if (err)
83 89 goto error;
84 90  
... ... @@ -97,8 +103,11 @@
97 103 * Restore raw mode, in any case; we *must* ignore any error apart
98 104 * EINTR, except for debug.
99 105 */
100   - if (isatty(fd))
  106 + if (isatty(fd)) {
101 107 CATCH_EINTR(tcsetattr(fd, TCSAFLUSH, &save));
  108 + sigprocmask(SIG_SETMASK, &old, NULL);
  109 + }
  110 +
102 111 return err;
103 112 error:
104 113 return -errno;