Messages in this thread Patch in this message | | | Date | Tue, 20 May 2008 12:45:56 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] block: blk_queue_bounce_limits can actually sleep |
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On Tue, 20 May 2008 21:29:59 +0200 Jens Axboe <jens.axboe@oracle.com> wrote:
> On Mon, May 19 2008, Arjan van de Ven wrote: > > From: Arjan van de Ven <arjan@linux.intel.com> > > 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:
foo() { ... if (some_unlikely_condition()) do_something_which_sleeps(); ... }
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???
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