linux-kernel - Re: [PATCH 4/7] nandsim: Don't use PF

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: <20091125084630.AFC5.A69D9226@jp.fujitsu.com>
Date:	Wed, 25 Nov 2009 09:42:16 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Adrian Hunter <adrian.hunter@...ia.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	"Bityutskiy Artem (Nokia-D/Helsinki)" <Artem.Bityutskiy@...ia.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Woodhouse <David.Woodhouse@...el.com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>
Subject: Re: [PATCH 4/7] nandsim: Don't use PF_MEMALLOC

> ext KOSAKI Motohiro wrote:
> > Hi
> > 
> > Thank you for this useful comments.
> > 
> >>> I vaguely remember Adrian (CCed) did this on purpose. This is for the
> >>> case when nandsim emulates NAND flash on top of a file. So there are 2
> >>> file-systems involved: one sits on top of nandsim (e.g. UBIFS) and the
> >>> other owns the file which nandsim uses (e.g., ext3).
> >>>
> >>> And I really cannot remember off the top of my head why he needed
> >>> PF_MEMALLOC, but I think Adrian wanted to prevent the direct reclaim
> >>> path to re-enter, say UBIFS, and cause deadlock. But I'd thing that all
> >>> the allocations in vfs_read()/vfs_write() should be GFP_NOFS, so that
> >>> should not be a probelm?
> >>>
> >> Yes it needs PF_MEMALLOC to prevent deadlock because there can be a
> >> file system on top of nandsim which, in this case, is on top of another
> >> file system.
> >>
> >> I do not see how mempools will help here.
> >>
> >> Please offer an alternative solution.
> > 
> > I have few questions.
> > 
> > Can you please explain more detail? Another stackable filesystam
> > (e.g. ecryptfs) don't have such problem. Why nandsim have its issue?
> > What lock cause deadlock?
> 
> The file systems are not stacked.  One is over nandsim, which nandsim
> does not know about because it is just a lowly NAND device, and, with
> the file cache option, one file system below to provide the file cache.
> 
> The deadlock is the kernel writing out dirty pages to the top file system
> which writes to nandsim which writes to the bottom file system which
> allocates memory which causes dirty pages to be written out to the top
> file system, which tries to write to nandsim => deadlock.

You mean you want to prevent pageout() instead reclaim itself?
Dropping filecache seems don't make recursive call, right?



--
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/