Messages in this thread Patch in this message | | | Date | Thu, 29 Sep 2005 19:20:18 -0700 | From | Chris Wright <> | Subject | [PATCH 02/10] [PATCH] Fix fs/exec.c:788 (de_thread()) BUG_ON |
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-stable review patch. If anyone has any objections, please let us know. ------------------
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> Signed-off-by: Chris Wright <chrisw@osdl.org> --- fs/exec.c | 5 ++--- 1 files changed, 2 insertions(+), 3 deletions(-)
Index: linux-2.6.13.y/fs/exec.c =================================================================== --- linux-2.6.13.y.orig/fs/exec.c +++ linux-2.6.13.y/fs/exec.c @@ -745,8 +745,8 @@ static inline int de_thread(struct task_ } /* - * Now there are really no other threads at all, - * so it's safe to stop telling them to kill themselves. + * There may be one thread left which is just exiting, + * but it's safe to stop telling the group to kill themselves. */ sig->flags = 0; @@ -785,7 +785,6 @@ no_thread_group: kmem_cache_free(sighand_cachep, oldsighand); } - BUG_ON(!thread_group_empty(current)); BUG_ON(!thread_group_leader(current)); return 0; } -- - 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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