linux-ext4 - Re: [PATCH v2 2/3] jbd2: Add extra parameter in start_this

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sun, 5 Jun 2011 17:12:24 -0700
From:	Manish Katiyar <mkatiyar@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	"Ted Ts'o" <tytso@....edu>, linux-ext4@...r.kernel.org,
	mfasheh@...e.com, jlbec@...lplan.org
Subject: Re: [PATCH v2 2/3] jbd2: Add extra parameter in start_this_handle()
 to control allocation flags.

On Thu, Jun 2, 2011 at 2:54 AM, Jan Kara <jack@...e.cz> wrote:
> On Tue 31-05-11 18:27:20, Ted Tso wrote:
>> On Tue, May 31, 2011 at 01:22:53PM +0200, Jan Kara wrote:
>> >
>> > The problem is that with ext4, we need i_mutex in io completion path to
>> > end page writeback. So we cannot do GFP_KERNEL allocation whenever we hold
>> > i_mutex because mm might wait in direct reclaim for IO to complete and that
>> > cannot happen until we release i_mutex.
>>
>> OK, maybe I'm being dense, but I'm not seeing it.  I see where we need
>> i_mutex on the ext4_da_writepages() codepath, but that's never used
>> for direct reclaim.  Direct reclaim only calls ext4_writepage(), and
>> that doesn't seem to try to grab i_mutex as near as I can tell.  Am I
>> missing something?
>  What happens is that direct reclaim sometimes does
> wait_on_page_writeback() (e.g. shrink_page_list()) or it explicitely waits
> for NR_WRITEBACK statistics to go below some threshold
> (throttle_vm_writeout()). And that is deadlockable if we hold i_mutex while
> doing this because we may need i_mutex to actually move the page from
> PageWriteback state...
>
> As I'm saying this, I've realized ext4 has this problem also with
> stable-pages patches because there we can wait for PageWriteback in
> grab_cache_page_write_begin() when we also hold i_mutex. So I think we'll
> have to come up with a way to convert unwritten extents without having to
> hold i_mutex. That's going to be interesting.

Hi Jan/Ted,

Does that mean I should remove the whole JBD2_TOPLEVEL thing from my
revised patch ? Or should I fix it as per your feedback in
the other patch ?

-- 
Thanks -
Manish
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html