From: Peter Zijlstra <peterz@infradead.org>
To: mingo@kernel.org
Cc: byungchul.park@lge.com, tj@kernel.org, boqun.feng@gmail.com,
david@fromorbit.com, johannes@sipsolutions.net, oleg@redhat.com,
linux-kernel@vger.kernel.org, peterz@infradead.org
Subject: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation
Date: Wed, 23 Aug 2017 13:58:47 +0200 [thread overview]
Message-ID: <20170823121432.990701317@infradead.org> (raw)
In-Reply-To: 20170823115843.662056844@infradead.org
[-- Attachment #1: peterz-lockdep-cross-fix.patch --]
[-- Type: text/plain, Size: 7685 bytes --]
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>
---
include/linux/irqflags.h | 4 +--
include/linux/lockdep.h | 8 +++---
kernel/locking/lockdep.c | 60 +++++++++++++++++++++++++++++------------------
kernel/workqueue.c | 23 +++++++++++++++++-
4 files changed, 66 insertions(+), 29 deletions(-)
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -26,7 +26,7 @@
# define trace_hardirq_enter() \
do { \
current->hardirq_context++; \
- crossrelease_hist_start(XHLOCK_HARD); \
+ crossrelease_hist_start(XHLOCK_HARD, 0);\
} while (0)
# define trace_hardirq_exit() \
do { \
@@ -36,7 +36,7 @@ do { \
# define lockdep_softirq_enter() \
do { \
current->softirq_context++; \
- crossrelease_hist_start(XHLOCK_SOFT); \
+ crossrelease_hist_start(XHLOCK_SOFT, 0);\
} while (0)
# define lockdep_softirq_exit() \
do { \
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -578,11 +578,11 @@ extern void lock_commit_crosslock(struct
#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 +591,11 @@ extern void lockdep_free_task(struct tas
#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
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -4629,7 +4629,7 @@ asmlinkage __visible void lockdep_sys_ex
* the index to point to the last entry, which is already invalid.
*/
crossrelease_hist_end(XHLOCK_PROC);
- crossrelease_hist_start(XHLOCK_PROC);
+ crossrelease_hist_start(XHLOCK_PROC, false);
}
void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
@@ -4725,25 +4725,25 @@ static inline void invalidate_xhlock(str
/*
* Lock history stacks; we have 3 nested lock history stacks:
*
- * Hard IRQ
- * Soft IRQ
- * History / Task
- *
- * The thing is that once we complete a (Hard/Soft) IRQ the future task locks
- * should not depend on any of the locks observed while running the IRQ.
- *
- * So what we do is rewind the history buffer and erase all our knowledge of
- * that temporal event.
- */
-
-/*
- * We need this to annotate lock history boundaries. Take for instance
- * workqueues; each work is independent of the last. The completion of a future
- * work does not depend on the completion of a past work (in general).
- * Therefore we must not carry that (lock) dependency across works.
+ * HARD(IRQ)
+ * SOFT(IRQ)
+ * PROC(ess)
+ *
+ * The thing is that once we complete a HARD/SOFT IRQ the future task locks
+ * should not depend on any of the locks observed while running the IRQ. So
+ * what we do is rewind the history buffer and erase all our knowledge of that
+ * temporal event.
+ *
+ * The PROCess one is special though; it is used to annotate independence
+ * inside a task.
+ *
+ * Take for instance workqueues; each work is independent of the last. The
+ * completion of a future work does not depend on the completion of a past work
+ * (in general). Therefore we must not carry that (lock) dependency across
+ * works.
*
* This is true for many things; pretty much all kthreads fall into this
- * pattern, where they have an 'idle' state and future completions do not
+ * pattern, where they have an invariant state and future completions do not
* depend on past completions. Its just that since they all have the 'same'
* form -- the kthread does the same over and over -- it doesn't typically
* matter.
@@ -4751,15 +4751,31 @@ static inline void invalidate_xhlock(str
* The same is true for system-calls, once a system call is completed (we've
* returned to userspace) the next system call does not depend on the lock
* history of the previous system call.
+ *
+ * They key property for independence, this invariant state, is that it must be
+ * a point where we hold no locks and have no history. Because if we were to
+ * hold locks, the restore at _end() would not necessarily recover it's history
+ * entry. Similarly, independence per-definition means it does not depend on
+ * prior state.
*/
-void crossrelease_hist_start(enum xhlock_context_t c)
+void crossrelease_hist_start(enum xhlock_context_t c, bool force)
{
struct task_struct *cur = current;
- if (cur->xhlocks) {
- cur->xhlock_idx_hist[c] = cur->xhlock_idx;
- cur->hist_id_save[c] = cur->hist_id;
+ if (!cur->xhlocks)
+ return;
+
+ /*
+ * We call this at an invariant point, no current state, no history.
+ */
+ if (c == XHLOCK_PROC) {
+ /* verified the former, ensure the latter */
+ WARN_ON_ONCE(!force && cur->lockdep_depth);
+ invalidate_xhlock(&xhlock(cur->xhlock_idx));
}
+
+ cur->xhlock_idx_hist[c] = cur->xhlock_idx;
+ cur->hist_id_save[c] = cur->hist_id;
}
void crossrelease_hist_end(enum xhlock_context_t c)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2093,7 +2093,28 @@ __acquires(&pool->lock)
lock_map_acquire(&pwq->wq->lockdep_map);
lock_map_acquire(&lockdep_map);
- crossrelease_hist_start(XHLOCK_PROC);
+ /*
+ * Strictly speaking we should do start(PROC) without holding any
+ * locks, that is, before these two lock_map_acquire()'s.
+ *
+ * However, that would result in:
+ *
+ * A(W1)
+ * WFC(C)
+ * A(W1)
+ * C(C)
+ *
+ * Which would create W1->C->W1 dependencies, even though there is no
+ * actual deadlock possible. There are two solutions, using a
+ * read-recursive acquire on the work(queue) 'locks', but this will then
+ * hit the lockdep limitation on recursive locks, or simly discard
+ * these locks.
+ *
+ * AFAICT there is no possible deadlock scenario between the
+ * flush_work() and complete() primitives (except for single-threaded
+ * workqueues), so hiding them isn't a problem.
+ */
+ crossrelease_hist_start(XHLOCK_PROC, true);
trace_workqueue_execute_start(work);
worker->current_func(work);
/*
next prev parent reply other threads:[~2017-08-23 12:19 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-23 11:58 [PATCH 0/4] workqueue and lockdep stuffs Peter Zijlstra
2017-08-23 11:58 ` [PATCH 1/4] workqueue: Use TASK_IDLE Peter Zijlstra
2017-08-23 13:31 ` Tejun Heo
2017-08-23 11:58 ` [PATCH 2/4] lockdep/selftests: Add mixed read-write ABBA tests Peter Zijlstra
2017-08-23 11:58 ` [PATCH 3/4] workqueue/lockdep: Fix flush_work() annotation Peter Zijlstra
2017-08-23 11:58 ` Peter Zijlstra [this message]
2017-08-24 2:18 ` [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park
2017-08-24 14:02 ` Peter Zijlstra
2017-08-25 1:11 ` Byungchul Park
2017-08-29 8:59 ` Peter Zijlstra
2017-08-29 14:23 ` [tip:locking/core] locking/lockdep: Untangle xhlock history save/restore from task independence tip-bot for Peter Zijlstra
2017-08-29 16:02 ` [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park
2017-08-29 18:47 ` Peter Zijlstra
2017-08-30 2:09 ` Byungchul Park
2017-08-30 7:41 ` Byungchul Park
2017-08-30 8:53 ` Peter Zijlstra
2017-08-30 9:01 ` Byungchul Park
2017-08-30 9:12 ` Peter Zijlstra
2017-08-30 9:14 ` Peter Zijlstra
2017-08-30 9:35 ` Byungchul Park
2017-08-30 9:24 ` Byungchul Park
2017-08-30 11:25 ` Byungchul Park
2017-08-30 12:49 ` Byungchul Park
2017-08-31 7:26 ` Byungchul Park
2017-08-31 8:04 ` Peter Zijlstra
2017-08-31 8:15 ` Byungchul Park
2017-08-31 8:34 ` Peter Zijlstra
2017-09-01 2:05 ` Byungchul Park
2017-09-01 9:47 ` Peter Zijlstra
2017-09-01 10:16 ` Byungchul Park
2017-09-01 12:09 ` 박병철/선임연구원/SW Platform(연)AOT팀(byungchul.park@lge.com)
2017-09-01 12:38 ` Peter Zijlstra
2017-09-01 13:51 ` Byungchul Park
2017-09-01 16:38 ` Peter Zijlstra
2017-09-04 1:30 ` Byungchul Park
2017-09-04 2:08 ` Byungchul Park
2017-09-04 11:42 ` Peter Zijlstra
2017-09-05 0:38 ` Byungchul Park
2017-09-05 7:08 ` Peter Zijlstra
2017-09-05 7:19 ` Peter Zijlstra
2017-09-05 8:57 ` Byungchul Park
2017-09-05 9:36 ` Peter Zijlstra
2017-09-05 10:31 ` Byungchul Park
2017-09-05 10:52 ` Peter Zijlstra
2017-09-05 11:24 ` Byungchul Park
2017-09-05 10:58 ` Byungchul Park
2017-09-05 13:46 ` Peter Zijlstra
2017-09-05 23:52 ` Byungchul Park
2017-09-06 0:42 ` Boqun Feng
2017-09-06 1:32 ` Byungchul Park
2017-09-06 23:59 ` Byungchul Park
2017-09-07 0:11 ` Byungchul Park
2017-09-06 0:48 ` Byungchul Park
2017-09-05 8:30 ` Byungchul Park
2017-08-31 8:07 ` Peter Zijlstra
2017-08-25 4:39 ` Byungchul Park
2017-08-29 6:46 ` Byungchul Park
2017-08-29 9:01 ` Peter Zijlstra
2017-08-29 16:12 ` Byungchul Park
2017-08-23 13:32 ` [PATCH 0/4] workqueue and lockdep stuffs Tejun Heo
2017-08-23 13:45 ` Peter Zijlstra
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