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

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Date:	Tue, 15 Jun 2010 17:56:34 +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

Hello Jamie,

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.
> 
> Perhaps MIPS udelay() should be disabling preemption itself, or
> (as x86 does) using raw_smp_processor_id() instead?

Sorry for the noise. I now find that raw_smp_processor_id() has been
implemented specific to MIPS in the latest kernel, I was using 2.6.32.

Thanks and regards,
Philby

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