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| author | Stefan Richter <stefanr@s5r6.in-berlin.de> | 2010-08-19 14:13:43 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-08-20 09:34:56 -0700 |
| commit | 1ee41680572971e34d90d5f584daf33195ec6dcb (patch) | |
| tree | f34cc8afcba020e0b47e676b5583e5d59fc26306 /Documentation | |
| parent | 626115cda9a31d7618cfd5ca8928811e5947d360 (diff) | |
| download | lwn-1ee41680572971e34d90d5f584daf33195ec6dcb.tar.gz lwn-1ee41680572971e34d90d5f584daf33195ec6dcb.zip | |
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.tmpl | 7 |
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 --- 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> |