linux-kernel - Re: [PATCH] mtd: Fix bug using smp_processor_id() in preemptible ubi

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:	Mon, 14 Jun 2010 22:10:18 +0530
From:	Philby John <pjohn@...sta.com>
To:	Jamie Lokier <jamie@...reable.org>
Cc:	linux-mtd@...ts.infradead.org, linux-mips@...ux-mips.org,
	David Daney <ddaney@...iumnetworks.com>,
	linux-kernel@...r.kernel.org,
	Artem Bityutskiy <dedekind1@...il.com>
Subject: Re: [PATCH] mtd: Fix bug using smp_processor_id() in preemptible
 ubi_bgt1d kthread

On Mon, 2010-06-14 at 16:04 +0100, Jamie Lokier wrote:
> Philby John wrote:
> > mtd: Fix bug using smp_processor_id() in preemptible ubi_bgt1d kthread
> > 
> > On a MIPS Cavium Octeon CN5020 when trying to create a UBI volume,
> > on the NOR flash, the kernel thread ubi_bgt1d calls
> > cfi_amdstd_write_buffers() --> do_write_buffer() -->
> > INVALIDATE_CACHE_UDELAY --> __udelay(). Its __udelay() that calls
> > smp_processor_id() in preemptible code, which you are not supposed to.
> > Fix the problem by disabling preemption.
> 
> The MTD code just calls udelay().
> Are you sure it isn't permitted to call udelay() from preemptible code?
> I think it is fine.

It isn't really udelay() but smp_processor_id() that you are not to call
from a preemptible thread. Now I also see Ed Swierk has done a similar
thing https://patchwork.kernel.org/patch/4049/ and he comments "..which
calls smp_processor_id(), which is not supposed to be called from a
preemptible thread."


So perhaps I can use preempt_disable() around just this call in function
__udelay()?

Regards,
Philby

--
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/