Messages in this thread Patch in this message | | | Date | Fri, 04 Sep 2009 17:14:31 -0700 | From | Greg KH <> | Subject | [patch 56/71] kthreads: fix kthread_create() vs kthread_stop() race |
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2.6.30-stable review patch. If anyone has any objections, please let us know.
------------------ From: Oleg Nesterov <oleg@redhat.com>
The bug should be "accidently" fixed by recent changes in 2.6.31, all kernels <= 2.6.30 need the fix. The problem was never noticed before, it was found because it causes mysterious failures with GFS mount/umount.
Credits to Robert Peterson. He blaimed kthread.c from the very beginning. But, despite my promise, I forgot to inspect the old implementation until he did a lot of testing and reminded me. This led to huge delay in fixing this bug.
kthread_stop() does put_task_struct(k) before it clears kthread_stop_info.k. This means another kthread_create() can re-use this task_struct, but the new kthread can still see kthread_should_stop() == T and exit even without calling threadfn().
Reported-by: Robert Peterson <rpeterso@redhat.com> Tested-by: Robert Peterson <rpeterso@redhat.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- kernel/kthread.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -216,12 +216,12 @@ int kthread_stop(struct task_struct *k) /* Now set kthread_should_stop() to true, and wake it up. */ kthread_stop_info.k = k; wake_up_process(k); - put_task_struct(k); /* Once it dies, reset stop ptr, gather result and we're done. */ wait_for_completion(&kthread_stop_info.done); kthread_stop_info.k = NULL; ret = kthread_stop_info.err; + put_task_struct(k); mutex_unlock(&kthread_stop_lock); trace_sched_kthread_stop_ret(ret);
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