Re: [PATCH] Busy inodes after unmount, be more verbose in generic_shutdown_super

From: Kirill Korotaev <dev@sw.ru>
To: Neil Brown <neilb@suse.de>
Cc: Balbir Singh <bsingharora@gmail.com>,
	linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>,
	Olaf Hering <olh@suse.de>, Jan Blunck <jblunck@suse.de>,
	Kirill Korotaev <dev@openvz.org>, Al Viro <viro@ftp.linux.org.uk>
Subject: Re: [PATCH] Busy inodes after unmount, be more verbose in generic_shutdown_super
Date: Tue, 07 Mar 2006 09:16:22 +0300	[thread overview]
Message-ID: <440D2536.60005@sw.ru> (raw)
In-Reply-To: <17420.59580.915759.44913@cse.unsw.edu.au>

>>The code changes look big, have you looked at
>>http://marc.theaimsgroup.com/?l=linux-kernel&m=113817279225962&w=2
> 
> 
> No I haven't.  I like it.
>  - Holding the semaphore shouldn't be a problem.
>  - calling down_read_trylock ought to be fast
>  - I *think* the unwanted calls to prune_dcache are always under
>    PF_MEMALLOC - they certainly seem to be.
No, it looks as it is not :(
Have you noticed my comment about "count" argument to prune_dcache()?
For example, prune_dcache() is called from shrink_dcache_parent() which 
is called in many places and not all of them have PF_MEMALLOC or 
s_umount semaphore for write. But prune_dcache() doesn't care for super 
blocks etc. It simply shrinks N dentries which are found _first_.

So the condition:
+		if ((current->flags & PF_MEMALLOC) &&
+			!(ret = down_read_trylock(&s->s_umount))) {
is not always true when the race occurs, as PF_MEMALLOC is not always set.

> And it is a nice small change.
> Have you had any other feedback on this?
here it is :)

Thanks,
Kirill