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authorAlexander Nyberg <alexn@telia.com>2005-09-14 18:54:06 +0200
committerLinus Torvalds <torvalds@g5.osdl.org>2005-09-14 10:26:34 -0700
commitfb085cf1d4294824571815d487daccc0609543f0 (patch)
treee3a704026e65bf6fea0c7747f0fb75a506f54127 /fs/exec.c
parent32a3658533c6f4c6bf370dd730213e802464ef9b (diff)
downloadlwn-fb085cf1d4294824571815d487daccc0609543f0.tar.gz
lwn-fb085cf1d4294824571815d487daccc0609543f0.zip
[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>
Diffstat (limited to 'fs/exec.c')
-rw-r--r--fs/exec.c5
1 files changed, 2 insertions, 3 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 14dd03907ccb..6fae59a22b43 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -745,8 +745,8 @@ static inline int de_thread(struct task_struct *tsk)
}
/*
- * 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;
}