Re: [PATCH] block: blk_queue_bounce_limits can actually sleep
From: Arjan van de Ven
Date: Tue May 20 2008 - 16:04:44 EST
On Tue, 20 May 2008 12:45:56 -0700
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Tue, 20 May 2008 21:29:59 +0200
> Jens Axboe <jens.axboe@xxxxxxxxxx> wrote:
> > On Mon, May 19 2008, Arjan van de Ven wrote:
> > > From: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
> > > Subject: [PATCH] block: blk_queue_bounce_limits can actually sleep
> > >
> > > blk_queue_bounce_limit can call init_emergency_isa_pool, which
> > > does sleeping allocations... document it as such by adding
> > > might_sleep() to the driver
> > Isn't that superflous, as mempool_create() -> kmalloc(...,
> > __GFP_WAIT) ends up spewing that warning anyway?
> It's largely superfluous given the way in which Arjan implemented it.
> One situation which we regularly hit is:
> if (some_unlikely_condition())
> and then we go and call that code under spinlock and ship it out, when
> of course a handful of testers hit the unlikely condition.
> The solution to that is to add a might_sleep() _outside_ the test of
> some_unlikely_condition(). ie:
> --- a/block/blk-settings.c~a
> +++ a/block/blk-settings.c
> @@ -140,6 +140,8 @@ void blk_queue_bounce_limit(struct reque
> unsigned long b_pfn = dma_addr >> PAGE_SHIFT;
> int dma = 0;
> + might_sleep();
> q->bounce_gfp = GFP_NOIO;
> #if BITS_PER_LONG == 64
> /* Assume anything <= 4GB can be handled by IOMMU.
> but it's all vague and waffly because Arjan forgot to tell us why he's
> bothering to patch this code at all???
the sata_nv driver calls this from an invalid context ... and spews a
ton of warnings as a result... made me think this is a common mistake
I'd love to make it do your version instead, but I was afraid it would
trigger too often....
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