diff options
| author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2009-06-19 17:39:33 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-06-19 17:57:36 +0200 |
| commit | b49a9e7e72103ea91946453c19703a4dfa1994fe (patch) | |
| tree | 7e9e74881384c581afca56cc397901f71e904c8b | |
| parent | 0c87197142427063e096f11603543ca874045952 (diff) | |
perf_counter: Close race in perf_lock_task_context()
perf_lock_task_context() is buggy because it can return a dead
context.
the RCU read lock in perf_lock_task_context() only guarantees
the memory won't get freed, it doesn't guarantee the object is
valid (in our case refcount > 0).
Therefore we can return a locked object that can get freed the
moment we release the rcu read lock.
perf_pin_task_context() then increases the refcount and does an
unlock on freed memory.
That increased refcount will cause a double free, in case it
started out with 0.
Ammend this by including the get_ctx() functionality in
perf_lock_task_context() (all users already did this later
anyway), and return a NULL context when the found one is
already dead.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
| -rw-r--r-- | kernel/perf_counter.c | 11 |
1 files changed, 5 insertions, 6 deletions
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c index 8d4f0dd41c22..adb6ae506d5b 100644 --- a/kernel/perf_counter.c +++ b/kernel/perf_counter.c @@ -175,6 +175,11 @@ perf_lock_task_context(struct task_struct *task, unsigned long *flags) spin_unlock_irqrestore(&ctx->lock, *flags); goto retry; } + + if (!atomic_inc_not_zero(&ctx->refcount)) { + spin_unlock_irqrestore(&ctx->lock, *flags); + ctx = NULL; + } } rcu_read_unlock(); return ctx; @@ -193,7 +198,6 @@ static struct perf_counter_context *perf_pin_task_context(struct task_struct *ta ctx = perf_lock_task_context(task, &flags); if (ctx) { ++ctx->pin_count; - get_ctx(ctx); spin_unlock_irqrestore(&ctx->lock, flags); } return ctx; @@ -1459,11 +1463,6 @@ static struct perf_counter_context *find_get_context(pid_t pid, int cpu) put_ctx(parent_ctx); ctx->parent_ctx = NULL; /* no longer a clone */ } - /* - * Get an extra reference before dropping the lock so that - * this context won't get freed if the task exits. - */ - get_ctx(ctx); spin_unlock_irqrestore(&ctx->lock, flags); } |