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| author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2009-08-07 21:49:01 +0400 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-08-09 14:54:46 +0400 |
| commit | 3a80b4a3539696f4b0574876326860323035a302 (patch) | |
| tree | 9d2901259a2b25b181997f89495452fd7f06827b | |
| parent | 3a43ce68ae1758fa6a839386025ef45acb6baa22 (diff) | |
| download | linux-3a80b4a3539696f4b0574876326860323035a302.tar.xz | |
perf_counter: Fix a race on perf_counter_ctx
While extending perfcounters with BTS hw-tracing, Markus
Metzger managed to trigger this warning:
[ 995.557128] WARNING: at kernel/perf_counter.c:1191 __perf_counter_task_sched_out+0x48/0x6b()
triggers because commit
9f498cc5be7e013d8d6e4c616980ed0ffc8680d2 (perf_counter: Full
task tracing) removed clearing of tsk->perf_counter_ctxp out
from under ctx->lock which introduced a race (against
perf_lock_task_context).
Move it back and deal with the exit notification by explicitly
passing along the former task context.
Reported-by: Markus T Metzger <markus.t.metzger@intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1249667341.17467.5.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
| -rw-r--r-- | kernel/perf_counter.c | 30 |
1 files changed, 15 insertions, 15 deletions
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c index 002310540417..546e62d62941 100644 --- a/kernel/perf_counter.c +++ b/kernel/perf_counter.c @@ -2850,7 +2850,8 @@ perf_counter_read_event(struct perf_counter *counter, */ struct perf_task_event { - struct task_struct *task; + struct task_struct *task; + struct perf_counter_context *task_ctx; struct { struct perf_event_header header; @@ -2910,24 +2911,23 @@ static void perf_counter_task_ctx(struct perf_counter_context *ctx, static void perf_counter_task_event(struct perf_task_event *task_event) { struct perf_cpu_context *cpuctx; - struct perf_counter_context *ctx; + struct perf_counter_context *ctx = task_event->task_ctx; cpuctx = &get_cpu_var(perf_cpu_context); perf_counter_task_ctx(&cpuctx->ctx, task_event); put_cpu_var(perf_cpu_context); rcu_read_lock(); - /* - * doesn't really matter which of the child contexts the - * events ends up in. - */ - ctx = rcu_dereference(current->perf_counter_ctxp); + if (!ctx) + ctx = rcu_dereference(task_event->task->perf_counter_ctxp); if (ctx) perf_counter_task_ctx(ctx, task_event); rcu_read_unlock(); } -static void perf_counter_task(struct task_struct *task, int new) +static void perf_counter_task(struct task_struct *task, + struct perf_counter_context *task_ctx, + int new) { struct perf_task_event task_event; @@ -2937,8 +2937,9 @@ static void perf_counter_task(struct task_struct *task, int new) return; task_event = (struct perf_task_event){ - .task = task, - .event = { + .task = task, + .task_ctx = task_ctx, + .event = { .header = { .type = new ? PERF_EVENT_FORK : PERF_EVENT_EXIT, .misc = 0, @@ -2956,7 +2957,7 @@ static void perf_counter_task(struct task_struct *task, int new) void perf_counter_fork(struct task_struct *task) { - perf_counter_task(task, 1); + perf_counter_task(task, NULL, 1); } /* @@ -4310,7 +4311,7 @@ void perf_counter_exit_task(struct task_struct *child) unsigned long flags; if (likely(!child->perf_counter_ctxp)) { - perf_counter_task(child, 0); + perf_counter_task(child, NULL, 0); return; } @@ -4330,6 +4331,7 @@ void perf_counter_exit_task(struct task_struct *child) * incremented the context's refcount before we do put_ctx below. */ spin_lock(&child_ctx->lock); + child->perf_counter_ctxp = NULL; /* * If this context is a clone; unclone it so it can't get * swapped to another process while we're removing all @@ -4343,9 +4345,7 @@ void perf_counter_exit_task(struct task_struct *child) * won't get any samples after PERF_EVENT_EXIT. We can however still * get a few PERF_EVENT_READ events. */ - perf_counter_task(child, 0); - - child->perf_counter_ctxp = NULL; + perf_counter_task(child, child_ctx, 0); /* * We can recurse on the same lock type through: |