linux-kernel - Re: [PATCH 1/4] SUNRPC: spin svc_rqst initialization to its own function

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Date:	Fri, 18 Jan 2008 16:48:44 -0500
From:	Jeff Layton <jlayton@...hat.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	neilb@...e.de, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] SUNRPC: spin svc_rqst initialization to its own
 function

On Fri, 18 Jan 2008 15:59:43 -0500
"J. Bruce Fields" <bfields@...ldses.org> wrote:

> On Mon, Jan 14, 2008 at 09:05:15AM -0500, Jeff Layton wrote:
> > Move the initialzation in __svc_create_thread that happens prior to
> > thread creation to a new function. Export the function to allow
> > services to have better control over the svc_rqst structs.
> > 
> > Also rearrange the rqstp initialization to prevent NULL pointer
> > dereferences in svc_exit_thread in case allocations fail.
> 
> Those NULL dereferences are from the
> 
> 	list_del(&rqstp->rq_all);
> 
> ?  OK, make sense.  Thanks!
> 
> --b.
> 

Sorry, I didn't explain that well...

This was the problem that Neil pointed out with the existing code. If
the rqstp kzalloc succeeds, but the later kmallocs in
__svc_create_thread fail, we goto here:

    out_thread:
            svc_exit_thread(rqstp);

svc_exit_thread does this:

    struct svc_pool *pool = rqstp->rq_pool;

...and then later:

   spin_lock_bh(&pool->sp_lock);

...but rq_pool is set after the kmallocs, so if they fail rq_pool will
be NULL, and we'll oops in that spin_lock_bh().

The fix is to move the kmallocs closer to the bottom in the new
svc_prepare_thread function.

Thanks,
-- 
Jeff Layton <jlayton@...hat.com>
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