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Date: Tue, 29 Aug 2017 10:59:39 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Byungchul Park <byungchul.park@....com>
Cc: mingo@...nel.org, tj@...nel.org, boqun.feng@...il.com,
david@...morbit.com, johannes@...solutions.net, oleg@...hat.com,
linux-kernel@...r.kernel.org, kernel-team@....com
Subject: Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation
On Fri, Aug 25, 2017 at 10:11:14AM +0900, Byungchul Park wrote:
> I meant, this seems to be led from your mis-understanding of
> crossrelease_hist_{start, end}().
I have, several times now, explained why PROC is special.
You seem to still think it can be used like the soft/hard-irq ones, this
is fundamentally not so.
Does something like so help?
---
Subject: lockdep: Untangle xhlock history save/restore from task independence
Where XHLOCK_{SOFT,HARD} are save/restore points in the xhlocks[] to
ensure the temporal IRQ events don't interact with task state, the
XHLOCK_PROC is a fundament different beast that just happens to share
the interface.
The purpose of XHLOCK_PROC is to annotate independent execution inside
one task. For example workqueues, each work should appear to run in its
own 'pristine' 'task'.
Remove XHLOCK_PROC in favour of its own interface to avoid confusion.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
include/linux/irqflags.h | 4 +--
include/linux/lockdep.h | 7 +++--
kernel/locking/lockdep.c | 79 +++++++++++++++++++++++-------------------------
kernel/workqueue.c | 9 +++---
4 files changed, 48 insertions(+), 51 deletions(-)
diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 9bc050bc81b2..5fdd93bb9300 100644
--- 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, 0);\
+ crossrelease_hist_start(XHLOCK_HARD); \
} 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, 0);\
+ crossrelease_hist_start(XHLOCK_SOFT); \
} while (0)
# define lockdep_softirq_exit() \
do { \
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 78bb7133abed..bfa8e0b0d6f1 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -551,7 +551,6 @@ struct pin_cookie { };
enum xhlock_context_t {
XHLOCK_HARD,
XHLOCK_SOFT,
- XHLOCK_PROC,
XHLOCK_CTX_NR,
};
@@ -580,8 +579,9 @@ 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, bool force);
+extern void crossrelease_hist_start(enum xhlock_context_t c);
extern void crossrelease_hist_end(enum xhlock_context_t c);
+extern void lockdep_invariant_state(bool force);
extern void lockdep_init_task(struct task_struct *task);
extern void lockdep_free_task(struct task_struct *task);
#else /* !CROSSRELEASE */
@@ -593,8 +593,9 @@ 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, bool force) {}
+static inline void crossrelease_hist_start(enum xhlock_context_t c) {}
static inline void crossrelease_hist_end(enum xhlock_context_t c) {}
+static inline void lockdep_invariant_state(bool force) {}
static inline void lockdep_init_task(struct task_struct *task) {}
static inline void lockdep_free_task(struct task_struct *task) {}
#endif /* CROSSRELEASE */
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index f73ca595b81e..44c8d0d17170 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -4623,13 +4623,8 @@ asmlinkage __visible void lockdep_sys_exit(void)
/*
* The lock history for each syscall should be independent. So wipe the
* slate clean on return to userspace.
- *
- * crossrelease_hist_end() works well here even when getting here
- * without starting (i.e. just after forking), because it rolls back
- * the index to point to the last entry, which is already invalid.
*/
- crossrelease_hist_end(XHLOCK_PROC);
- crossrelease_hist_start(XHLOCK_PROC, false);
+ lockdep_invariant_state(false);
}
void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
@@ -4723,19 +4718,47 @@ static inline void invalidate_xhlock(struct hist_lock *xhlock)
}
/*
- * Lock history stacks; we have 3 nested lock history stacks:
+ * Lock history stacks; we have 2 nested lock history stacks:
*
* 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.
+ */
+
+void crossrelease_hist_start(enum xhlock_context_t c)
+{
+ struct task_struct *cur = current;
+
+ if (!cur->xhlocks)
+ return;
+
+ 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)
+{
+ struct task_struct *cur = current;
+
+ if (cur->xhlocks) {
+ unsigned int idx = cur->xhlock_idx_hist[c];
+ struct hist_lock *h = &xhlock(idx);
+
+ cur->xhlock_idx = idx;
+
+ /* Check if the ring was overwritten. */
+ if (h->hist_id != cur->hist_id_save[c])
+ invalidate_xhlock(h);
+ }
+}
+
+/*
+ * lockdep_invariant_state() is used to annotate independence inside a task, to
+ * make one task look like multiple independent 'tasks'.
*
* 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
@@ -4758,40 +4781,14 @@ static inline void invalidate_xhlock(struct hist_lock *xhlock)
* entry. Similarly, independence per-definition means it does not depend on
* prior state.
*/
-void crossrelease_hist_start(enum xhlock_context_t c, bool force)
+void lockdep_invariant_state(bool force)
{
- struct task_struct *cur = current;
-
- if (!cur->xhlocks)
- return;
-
/*
* We call this at an invariant point, no current state, no history.
+ * Verify the former, enforce the latter.
*/
- 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)
-{
- struct task_struct *cur = current;
-
- if (cur->xhlocks) {
- unsigned int idx = cur->xhlock_idx_hist[c];
- struct hist_lock *h = &xhlock(idx);
-
- cur->xhlock_idx = idx;
-
- /* Check if the ring was overwritten. */
- if (h->hist_id != cur->hist_id_save[c])
- invalidate_xhlock(h);
- }
+ WARN_ON_ONCE(!force && current->lockdep_depth);
+ invalidate_xhlock(&xhlock(current->xhlock_idx));
}
static int cross_lock(struct lockdep_map *lock)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index c0331891dec1..ab3c0dc8c7ed 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2094,8 +2094,8 @@ __acquires(&pool->lock)
lock_map_acquire(&pwq->wq->lockdep_map);
lock_map_acquire(&lockdep_map);
/*
- * Strictly speaking we should do start(PROC) without holding any
- * locks, that is, before these two lock_map_acquire()'s.
+ * Strictly speaking we should mark the invariant state without holding
+ * any locks, that is, before these two lock_map_acquire()'s.
*
* However, that would result in:
*
@@ -2107,14 +2107,14 @@ __acquires(&pool->lock)
* 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
+ * hit the lockdep limitation on recursive locks, or simply 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);
+ lockdep_invariant_state(true);
trace_workqueue_execute_start(work);
worker->current_func(work);
/*
@@ -2122,7 +2122,6 @@ __acquires(&pool->lock)
* point will only record its address.
*/
trace_workqueue_execute_end(work);
- crossrelease_hist_end(XHLOCK_PROC);
lock_map_release(&lockdep_map);
lock_map_release(&pwq->wq->lockdep_map);
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