|author||Stefan Richter <email@example.com>||2010-08-19 14:13:43 -0700|
|committer||Linus Torvalds <firstname.lastname@example.org>||2010-08-20 09:34:56 -0700|
Documentation: kernel-locking: mutex_trylock cannot be used in interrupt context
Chapter 6 is right about mutex_trylock, but chapter 10 wasn't. This error was introduced during semaphore-to-mutex conversion of the Unreliable guide. :-) If user context which performs mutex_lock() or mutex_trylock() is preempted by interrupt context which performs mutex_trylock() on the same mutex instance, a deadlock occurs. This is because these functions do not disable local IRQs when they operate on mutex->wait_lock. Signed-off-by: Stefan Richter <email@example.com> Acked-by: Rusty Russell <firstname.lastname@example.org> Cc: Matthew Wilcox <email@example.com> Cc: Randy Dunlap <firstname.lastname@example.org> Signed-off-by: Andrew Morton <email@example.com> Signed-off-by: Linus Torvalds <firstname.lastname@example.org>
1 files changed, 5 insertions, 2 deletions
diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl
index 084f6ad7b7a0..0b1a3f97f285 100644
@@ -1922,9 +1922,12 @@ machines due to caching.
- There is a <function>mutex_trylock()</function> which can be
- used inside interrupt context, as it will not sleep.
+ There is a <function>mutex_trylock()</function> which does not
+ sleep. Still, it must not be used inside interrupt context since
+ its implementation is not safe for that.
<function>mutex_unlock()</function> will also never sleep.
+ It cannot be used in interrupt context either since a mutex
+ must be released by the same task that acquired it.