From: Oleg Nesterov <oleg@tv-sign.ru>
Date: Wed, 22 Aug 2007 21:01:58 +0000 (-0700)
Subject: exec: kill unsafe BUG_ON(sig->count) checks
X-Git-Tag: v2.6.23-rc4~42
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=abd96ecb298675a21c412a29f5de2f80174d5f18;p=pandora-kernel.git

exec: kill unsafe BUG_ON(sig->count) checks

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>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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