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locking/lockdep: Fix workqueue crossrelease annotation

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The new completion/crossrelease annotations interact unfavourable with
the extant flush_work()/flush_workqueue() annotations.

The problem is that when a single work class does:

  wait_for_completion(&C)

and

  complete(&C)

in different executions, we'll build dependencies like:

  lock_map_acquire(W)
  complete_acquire(C)

and

  lock_map_acquire(W)
  complete_release(C)

which results in the dependency chain: W->C->W, which lockdep thinks
spells deadlock, even though there is no deadlock potential since
works are ran concurrently.

One possibility would be to change the work 'lock' to recursive-read,
but that would mean hitting a lockdep limitation on recursive locks.
Also, unconditinoally switching to recursive-read here would fail to
detect the actual deadlock on single-threaded workqueues, which do
have a problem with this.

For now, forcefully disregard these locks for crossrelease.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: byungchul.park@lge.com
Cc: david@fromorbit.com
Cc: johannes@sipsolutions.net
Cc: oleg@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2017-08-23 13:23:30 +02:00 • committed by Ingo Molnar
parent a1d14934ea
commit e6f3faa734
4 changed files with 66 additions and 27 deletions
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10
include/linux/lockdep.h
View file

@ -18,6 +18,8 @@ extern int lock_stat;
#define MAX_LOCKDEP_SUBCLASSES 8UL
#include <linux/types.h>
#ifdef CONFIG_LOCKDEP
#include <linux/linkage.h>
@ -578,11 +580,11 @@ extern void lock_commit_crosslock(struct lockdep_map *lock);
#define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
{ .name = (_name), .key = (void *)(_key), .cross = 0, }
extern void crossrelease_hist_start(enum xhlock_context_t c);
extern void crossrelease_hist_start(enum xhlock_context_t c, bool force);
extern void crossrelease_hist_end(enum xhlock_context_t c);
extern void lockdep_init_task(struct task_struct *task);
extern void lockdep_free_task(struct task_struct *task);
#else
#else /* !CROSSRELEASE */
#define lockdep_init_map_crosslock(m, n, k, s) do {} while (0)
/*
* To initialize a lockdep_map statically use this macro.
@ -591,11 +593,11 @@ extern void lockdep_free_task(struct task_struct *task);
#define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
{ .name = (_name), .key = (void *)(_key), }
static inline void crossrelease_hist_start(enum xhlock_context_t c) {}
static inline void crossrelease_hist_start(enum xhlock_context_t c, bool force) {}
static inline void crossrelease_hist_end(enum xhlock_context_t c) {}
static inline void lockdep_init_task(struct task_struct *task) {}
static inline void lockdep_free_task(struct task_struct *task) {}
#endif
#endif /* CROSSRELEASE */
#ifdef CONFIG_LOCK_STAT