linux-kernel - Re: dirty balancing deadlock

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, 18 Feb 2007 16:25:14 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Miklos Szeredi <miklos@...redi.hu>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: dirty balancing deadlock

Andrew Morton wrote:
> On Sun, 18 Feb 2007 19:28:18 +0100 Miklos Szeredi <miklos@...redi.hu> wrote:
> 
>> I was testing the new fuse shared writable mmap support, and finding
>> that bash-shared-mapping deadlocks (which isn't so strange ;).  What
>> is more strange is that this is not an OOM situation at all, with
>> plenty of free and cached pages.
>>
>> A little more investigation shows that a similar deadlock happens
>> reliably with bash-shared-mapping on a loopback mount, even if only
>> half the total memory is used.
>>
>> The cause is slightly different in the two cases:
>>
>>   - loopback mount: allocation by the underlying filesystem is stalled
>>     on throttle_vm_writeout()
>>
>>   - fuse-loop: page dirtying on the underlying filesystem is stalled on
>>     balance_dirty_pages()
>>
>> In both cases the underlying fs is totally innocent, with no
>> dirty/writback pages, yet it's waiting for the global dirty+writeback
>> to go below the threshold, which obviously won't, until the
>> allocation/dirtying succeeds.
>>
>> I'm not quite sure what the solution is, and asking for thoughts.
> 
> But....  these things don't just throttle.  They also perform large amounts
> of writeback, which causes the dirty levels to subside.
> 
>>>From your description it appears that this writeback isn't happening, or
> isn't working.  How come?

Is the fuse daemon trying to do writeback to itself, perhaps?

That is, trying to write out data to the FUSE filesystem, for which
it is also the server.


-- 
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is.  Each group
calls the other unpatriotic.
-
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/