tree d3737ebe960d65152b7ee119b8b5a7ad2d59e09b
parent b090f9fa53d51c8a33370071de9e391919ee1fa7
author Arve Hjønnevåg <arve@android.com> 1234573644 +0100
committer Linus Torvalds <torvalds@linux-foundation.org> 1235254638 -0800

PM: Fix suspend_console and resume_console to use only one semaphore

This fixes a race where a thread acquires the console while the
console is suspended, and the console is resumed before this
thread releases it. In this case, the secondary console
semaphore would be left locked, and the primary semaphore would
be released twice. This in turn would cause the console switch
on suspend or resume to hang forever.

Note that suspend_console does not actually lock the console
for clients that use acquire_console_sem, it only locks it for
clients that use try_acquire_console_sem. If we change
suspend_console to fully lock the console, then the kernel
may deadlock on suspend. One client of try_acquire_console_sem
is acquire_console_semaphore_for_printk, which uses it to
prevent printk from using the console while it is suspended.

Signed-off-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Len Brown <lenb@kernel.org>
Cc: Greg KH <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>