linux-kernel - Re: 2.6.26-rc4: RIP find_pid

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Message-ID: <20080527173711.GA1458@tv-sign.ru>
Date:	Tue, 27 May 2008 21:37:11 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ibm.com>
Subject: Re: 2.6.26-rc4: RIP find_pid_ns+0x6b/0xa0

On 05/27, Oleg Nesterov wrote:
>
> But I agree, this race is pretty much theoretical.

Perhaps we have the unbalanced put_pid(), in that case "struct pid" will
be freed without waiting for a grace period.

Alexey, could you re-test with the patch below?

Oleg.

Add the temporary debugging code to catch the unbalanced put_pid()'s.
At least those which can free the "live" pid.

--- MM/kernel/pid.c~	2008-02-20 18:29:40.000000000 +0300
+++ MM/kernel/pid.c	2008-02-20 18:35:15.000000000 +0300
@@ -208,6 +208,10 @@ void put_pid(struct pid *pid)
 	ns = pid->numbers[pid->level].ns;
 	if ((atomic_read(&pid->count) == 1) ||
 	     atomic_dec_and_test(&pid->count)) {
+		int type = PIDTYPE_MAX;
+		while (--type >= 0)
+			if (WARN_ON(!hlist_empty(&pid->tasks[type])))
+				return;
 		kmem_cache_free(ns->pid_cachep, pid);
 		put_pid_ns(ns);
 	}


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