linux-kernel - Re: Device loses barrier support (was: Fixed patch for simple barriers.)

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]

Message-ID: <20081204221551.GV6703@one.firstfloor.org>
Date:	Thu, 4 Dec 2008 23:15:51 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	xfs@....sgi.com, Alasdair G Kergon <agk@...hat.com>,
	Andi Kleen <andi-suse@...stfloor.org>,
	Milan Broz <mbroz@...hat.com>
Subject: Re: Device loses barrier support (was: Fixed patch for simple barriers.)

> If you are pushing what you are pushing --- barriers allowing to return 
> EOPNOTSUPP anytime --- then asynchronous barrier submits can no longer be 
> used, because by the time EOPNOTSUPP is detected, the filesystem is 
> already corrupted.

Chris Mason pointed out that this can actually already happen. From
a quick review this can happen in MD raid1 at least (their barriers_work
flag is pretty similar to the DM implementation I did).  So everyone
has to handle this already anyways.

> I'm wondering, where in fsync() does Linux wait for hardware disk cache to 
> be flushed? Isn't there a bug that fsync() will return before the cache is 
> flushed? I couldn't really find it. The last thing do_fsync calls is 
> filemap_fdatawait and it doesn't do cache flush (blkdev_issue_flush).

At least in fsync() on journaling fs the metadata update should push it.

-Andi

-- 
ak@...ux.intel.com
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/