[PATCH] Fix fs/exec.c:788 (de_thread()) BUG_ON
It turns out that the BUG_ON() in fs/exec.c: de_thread() is unreliable and can trigger due to the test itself being racy. de_thread() does while (atomic_read(&sig->count) > count) { } ..... ..... BUG_ON(!thread_group_empty(current)); but release_task does write_lock_irq(&tasklist_lock) __exit_signal (this is where atomic_dec(&sig->count) is run) __exit_sighand __unhash_process takes write lock on tasklist_lock remove itself out of PIDTYPE_TGID list write_unlock_irq(&tasklist_lock) so there's a clear (although small) window between the atomic_dec(&sig->count) and the actual PIDTYPE_TGID unhashing of the thread. And actually there is no need for all threads to have exited at this point, so we simply kill the BUG_ON. Big thanks to Marc Lehmann who provided the test-case. Fixes Bug 5170 (http://bugme.osdl.org/show_bug.cgi?id=5170) Signed-off-by: Alexander Nyberg <alexn@telia.com> Cc: Roland McGrath <roland@redhat.com> Cc: Andrew Morton <akpm@osdl.org> Cc: Ingo Molnar <mingo@elte.hu> Acked-by: Andi Kleen <ak@suse.de> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@ -745,8 +745,8 @@ static inline int de_thread(struct task_struct *tsk)
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}
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/*
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* Now there are really no other threads at all,
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* so it's safe to stop telling them to kill themselves.
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* There may be one thread left which is just exiting,
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* but it's safe to stop telling the group to kill themselves.
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*/
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sig->flags = 0;
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@ -785,7 +785,6 @@ no_thread_group:
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kmem_cache_free(sighand_cachep, oldsighand);
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}
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BUG_ON(!thread_group_empty(current));
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BUG_ON(!thread_group_leader(current));
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return 0;
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}
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