Messages in this thread | | | Date | Tue, 20 May 2008 13:03:57 -0700 | From | Arjan van de Ven <> | Subject | Re: [PATCH] block: blk_queue_bounce_limits can actually sleep |
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On Tue, 20 May 2008 12:45:56 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:
> 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???
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 to make.
I'd love to make it do your version instead, but I was afraid it would trigger too often....
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