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authorStefan Richter <stefanr@s5r6.in-berlin.de>2010-08-19 14:13:43 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-08-20 09:34:56 -0700
commit1ee41680572971e34d90d5f584daf33195ec6dcb (patch)
treef34cc8afcba020e0b47e676b5583e5d59fc26306 /Documentation
parent626115cda9a31d7618cfd5ca8928811e5947d360 (diff)
downloadlinux-linaro-android-1ee41680572971e34d90d5f584daf33195ec6dcb.tar.gz
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 <stefanr@s5r6.in-berlin.de> Acked-by: Rusty Russell <rusty@rustcorp.com.au> Cc: Matthew Wilcox <matthew@wil.cx> Cc: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/DocBook/kernel-locking.tmpl7
1 files changed, 5 insertions, 2 deletions
diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl
index 084f6ad7b7a..0b1a3f97f28 100644
--- a/Documentation/DocBook/kernel-locking.tmpl
+++ b/Documentation/DocBook/kernel-locking.tmpl
@@ -1922,9 +1922,12 @@ machines due to caching.
<function>mutex_lock()</function>
</para>
<para>
- 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.
</para>
</listitem>
</itemizedlist>