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locking: WW mutex cleanup

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Make the WW mutex code more readable by adding comments, splitting up
functions and pointing out that we're actually using the Wait-Die
algorithm.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Co-authored-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Ziljstra 2018-06-15 10:07:12 +02:00 • committed by Thomas Hellstrom
parent eab9766931
commit 55f036ca7e
3 changed files with 150 additions and 102 deletions
Download patch file Download diff file Expand all files Collapse all files

28
include/linux/ww_mutex.h
View file

@ -6,7 +6,7 @@
*
* Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
*
* Wound/wait implementation:
* Wait/Die implementation:
* Copyright (C) 2013 Canonical Ltd.
*
* This file contains the main data structure and API definitions.
@ -28,9 +28,9 @@ struct ww_class {
struct ww_acquire_ctx {
struct task_struct *task;
unsigned long stamp;
unsigned acquired;
unsigned int acquired;
#ifdef CONFIG_DEBUG_MUTEXES
unsigned done_acquire;
unsigned int done_acquire;
struct ww_class *ww_class;
struct ww_mutex *contending_lock;
#endif
@ -38,8 +38,8 @@ struct ww_acquire_ctx {
struct lockdep_map dep_map;
#endif
#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
unsigned deadlock_inject_interval;
unsigned deadlock_inject_countdown;
unsigned int deadlock_inject_interval;
unsigned int deadlock_inject_countdown;
#endif
};
@ -102,7 +102,7 @@ static inline void ww_mutex_init(struct ww_mutex *lock,
*
* Context-based w/w mutex acquiring can be done in any order whatsoever within
* a given lock class. Deadlocks will be detected and handled with the
* wait/wound logic.
* wait/die logic.
*
* Mixing of context-based w/w mutex acquiring and single w/w mutex locking can
* result in undetected deadlocks and is so forbidden. Mixing different contexts
@ -195,13 +195,13 @@ static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx)
* Lock the w/w mutex exclusively for this task.
*
* Deadlocks within a given w/w class of locks are detected and handled with the
* wait/wound algorithm. If the lock isn't immediately avaiable this function
* wait/die algorithm. If the lock isn't immediately available this function
* will either sleep until it is (wait case). Or it selects the current context
* for backing off by returning -EDEADLK (wound case). Trying to acquire the
* for backing off by returning -EDEADLK (die case). Trying to acquire the
* same lock with the same context twice is also detected and signalled by
* returning -EALREADY. Returns 0 if the mutex was successfully acquired.
*
* In the wound case the caller must release all currently held w/w mutexes for
* In the die case the caller must release all currently held w/w mutexes for
* the given context and then wait for this contending lock to be available by
* calling ww_mutex_lock_slow. Alternatively callers can opt to not acquire this
* lock and proceed with trying to acquire further w/w mutexes (e.g. when
@ -226,14 +226,14 @@ extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acq
* Lock the w/w mutex exclusively for this task.
*
* Deadlocks within a given w/w class of locks are detected and handled with the
* wait/wound algorithm. If the lock isn't immediately avaiable this function
* wait/die algorithm. If the lock isn't immediately available this function
* will either sleep until it is (wait case). Or it selects the current context
* for backing off by returning -EDEADLK (wound case). Trying to acquire the
* for backing off by returning -EDEADLK (die case). Trying to acquire the
* same lock with the same context twice is also detected and signalled by
* returning -EALREADY. Returns 0 if the mutex was successfully acquired. If a
* signal arrives while waiting for the lock then this function returns -EINTR.
*
* In the wound case the caller must release all currently held w/w mutexes for
* In the die case the caller must release all currently held w/w mutexes for
* the given context and then wait for this contending lock to be available by
* calling ww_mutex_lock_slow_interruptible. Alternatively callers can opt to
* not acquire this lock and proceed with trying to acquire further w/w mutexes
@ -256,7 +256,7 @@ extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
* @lock: the mutex to be acquired
* @ctx: w/w acquire context
*
* Acquires a w/w mutex with the given context after a wound case. This function
* Acquires a w/w mutex with the given context after a die case. This function
* will sleep until the lock becomes available.
*
* The caller must have released all w/w mutexes already acquired with the
@ -290,7 +290,7 @@ ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
* @lock: the mutex to be acquired
* @ctx: w/w acquire context
*
* Acquires a w/w mutex with the given context after a wound case. This function
* Acquires a w/w mutex with the given context after a die case. This function
* will sleep until the lock becomes available and returns 0 when the lock has
* been acquired. If a signal arrives while waiting for the lock then this
* function returns -EINTR.