linux-ext4 - Re: [patch] fix up lock order reversal in writeback

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:	Thu, 18 Nov 2010 12:22:38 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	Eric Sandeen <sandeen@...hat.com>, Nick Piggin <npiggin@...nel.dk>,
	"Ted Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>
Subject: Re: [patch] fix up lock order reversal in writeback

On Thu, 18 Nov 2010 13:51:15 -0500
Chris Mason <chris.mason@...cle.com> wrote:

> > If those functions "fix" a testcase then it was by sheer luck, and the
> > fs's ENOSPC handling is still busted.
> > 
> > For a start writeback_inodes_sb_if_idle() is a no-op if the device
> > isn't idle!  Secondly, if the device _was_ idle,
> > writeback_inodes_sb_if_idle() uses a work handoff to another thread,
> > which means that the work might not get executed for another six weeks.
> > 
> > So no, your ENOSPC handling is still busted and I'll be doing you a
> > favour when I send that parport patch.
> 
> Btrfs uses it with this cool looping construct. It's an innovative
> combination of while, 1, schedule_timeout(),  and if all goes well, break.

If the calling code can do that then it doesn't need to pass the work
off to another thread at all.  Just sychronously call
writeback_inodes_sb(), then bye-bye goes writeback_inodes_sb_if_idle(),
to great sighs of relief.

And again: as btrfs is effectively making a synchronous call to
writeback_inodes_sb() via schedule(), then surely it does not need to
take s_umount to protect its own darn superblock!!

--
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