Messages in this thread Patch in this message | | | Date | Sat, 18 Aug 2007 21:39:36 +0400 | From | Oleg Nesterov <> | Subject | [PATCH 1/5] exec: kill unsafe BUG_ON(sig->count) checks |
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de_thread:
if (atomic_read(&oldsighand->count) <= 1) BUG_ON(atomic_read(&sig->count) != 1);
This is not safe without the rmb() in between. The results of two correctly ordered __exit_signal()->atomic_dec_and_test()'s could be seen out of order on our CPU.
The same is true for the "thread_group_empty()" case, __unhash_process()'s changes could be seen before atomic_dec_and_test(&sig->count).
On some platforms (including i386) atomic_read() doesn't provide even the compiler barrier, in that case these checks are simply racy.
Remove these BUG_ON()'s. Alternatively, we can do something like
BUG_ON( ({ smp_rmb(); atomic_read(&sig->count) != 1; }) );
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
--- t/fs/exec.c~1_BUG_ON 2007-08-18 17:36:58.000000000 +0400 +++ t/fs/exec.c 2007-08-18 18:19:41.000000000 +0400 @@ -784,7 +784,6 @@ static int de_thread(struct task_struct * and we can just re-use it all. */ if (atomic_read(&oldsighand->count) <= 1) { - BUG_ON(atomic_read(&sig->count) != 1); signalfd_detach(tsk); exit_itimers(sig); return 0; @@ -929,8 +928,6 @@ no_thread_group: if (leader) release_task(leader); - BUG_ON(atomic_read(&sig->count) != 1); - if (atomic_read(&oldsighand->count) == 1) { /* * Now that we nuked the rest of the thread group, - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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