linux-kernel - Re: [PATCH resend] fs/proc: Move kfree outside pde_unload

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Message-ID: <20130405173623.GE4068@ZenIV.linux.org.uk>
Date:	Fri, 5 Apr 2013 18:36:23 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Nathan Zimmer <nzimmer@....com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	David Woodhouse <dwmw2@...radead.org>, stable@...r.kernel.org
Subject: Re: [PATCH resend] fs/proc: Move kfree outside pde_unload_lock

On Fri, Apr 05, 2013 at 12:05:26PM -0500, Nathan Zimmer wrote:
> On 04/04/2013 03:44 PM, Al Viro wrote:
> >On Thu, Apr 04, 2013 at 12:12:05PM -0500, Nathan Zimmer wrote:
> >
> >>Ok I am cloning the tree now.
> >>It does look like the patches would conflict.
> >>I'll run some tests and take a deeper look.
> >FWIW, I've just pushed there a tentative patch that switches to hopefully
> >saner locking (head should be at cb673c115c1f99d3480471ca5d8cb3f89a1e3bee).
> >Is that more or less what you want wrt spinlock contention?
> >
> >One note: for any given pde_opener, close_pdeo() can be called at most
> >by two threads - final fput() and remove_proc_entry() resp.  I think
> >the use of completion + flag is safe there; pde->pde_unload_lock
> >should serialize the critical areas.
> 
> Something isn't quite right.  I keep getting hung during boot.
> dracut: Mounted root filesystem /dev/sda8
> dracut: Switching root
> 
> I'll try to get some more info on a smaller box.

Umm...  Try to add WARN_ON(1) in entry_rundown(), just to see what's
getting hit (don't bother with entry name, stack trace will be enough).
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