linux-kernel - Re: Q: semaphore and kmalloc(GFP

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Message-Id: <20090511122046.B0ED.A69D9226@jp.fujitsu.com>
Date:	Mon, 11 May 2009 12:21:40 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: Q: semaphore and kmalloc(GFP_KERNEL)?

> KOSAKI Motohiro wrote:
> > > Can the kernel detect that we need to let kmalloc() fail and
> > > wake up the writer process so that the writer process releases
> > > the rw_semaphore and reader processes can continue?
> > 
> > it can't. Plus it shouldn't.
> > some caller don't want kmalloc() failure.
> 
> Thanks.
> Then, should I move kmalloc(GFP_KERNEL) to outside the lock whenever possible?

Yes. almost driver does it.
this is generic issue of nested locking.

> (I worry some lock held by the caller interferes kmalloc(GFP_KERNEL).)

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