linux-kernel - Re: [RFC][PATCH] Fix lock inversion aio_kick

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Message-ID: <x49velokztg.fsf@segfault.boston.devel.redhat.com>
Date:	Thu, 09 Nov 2006 17:41:47 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Zach Brown <zach.brown@...cle.com>
Cc:	Benjamin LaHaise <bcrl@...ck.org>, linux-kernel@...r.kernel.org,
	linux-aio@...ck.org, Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC][PATCH] Fix lock inversion aio_kick_handler()

==> On Fri, 28 Jul 2006 19:02:23 -0700, Zach Brown <zach.brown@...cle.com> said:

Zach> Benjamin LaHaise wrote:
Zach> > On Fri, Jul 28, 2006 at 05:10:32PM -0700, Zach Brown wrote:
Zach> >> Fix lock inversion aio_kick_handler()
Zach> > 
Zach> > Doh.  Unfortunately, this patch isn't entirely correct as it
Zach> could race with > __put_ioctx() which sets ioctx->mm = NULL.

Zach> Aha, yeah, that's what I was missing.  Thanks.

Zach> > Something like the following should do the trick:

Zach> Cool, I'll respin and send it out.

Did you ever resend this patch, Zach?  It doesn't appear to be in
current kernels.  I'm still running into the lockdep warnings.

-Jeff

--- linux-2.6.19-rc5-mm1/fs/aio.c.orig	2006-11-09 17:28:43.000000000 -0500
+++ linux-2.6.19-rc5-mm1/fs/aio.c	2006-11-09 17:29:29.000000000 -0500
@@ -864,13 +864,15 @@ static void aio_kick_handler(void *data)
 	struct kioctx *ctx = data;
 	mm_segment_t oldfs = get_fs();
 	int requeue;
+	struct mm_struct *mm;

 	set_fs(USER_DS);
 	use_mm(ctx->mm);
 	spin_lock_irq(&ctx->ctx_lock);
 	requeue =__aio_run_iocbs(ctx);
- 	unuse_mm(ctx->mm);
+	mm = ctx->mm;
 	spin_unlock_irq(&ctx->ctx_lock);
+ 	unuse_mm(mm);
 	set_fs(oldfs);
 	/*
 	 * we're in a worker thread already, don't use queue_delayed_work,
-
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