linux-kernel - Re: [PATCH 2/6] UBI: Fastmap: Ensure that only one fastmap work is scheduled

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, 27 Nov 2014 17:13:43 +0100
From:	Richard Weinberger <richard@....at>
To:	dedekind1@...il.com
CC:	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] UBI: Fastmap: Ensure that only one fastmap work is
 scheduled

Am 27.11.2014 um 16:27 schrieb Artem Bityutskiy:
> On Mon, 2014-11-24 at 14:20 +0100, Richard Weinberger wrote:
>> If the WL pool runs out of PEBs we schedule a fastmap write
>> to refill it as soon as possible.
>> Ensure that only one at a time is scheduled otherwise we might end in
>> a fastmap write storm because writing the fastmap can schedule another
>> write if bitflips are detected.
> 
> Could you please provide some more details about the "write storm". Does
> it happen when there are 2 fastmap works in the queue? Or if they run
> simultaneously? Why the storm happens and white kind of "writes" it
> consists of?

If UBI needs to write a new fastmap while wear leveling (by using get_peb_for_wl())
a fastmap work is scheduled.
We cannot write a fastmap in this context because we're in atomic context.
At this point one fastmap write is scheduled. If now get_peb_for_wl() is executed
a second time it will schedule another fastmap work because the pools are still not refilled.
This will go on until finally a fastmap got written. Either by the the kworker or
ubi_wl_get_peb().
As now a lot of fastmap works are scheduled they all will be issues in series.
Hence, a write storm. :)

Thanks,
//richard
--
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/