Messages in this thread Patch in this message | | | Date | Wed, 4 Nov 2009 07:34:38 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] prevent AoE causing cache aliases |
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On Wed, 04 Nov 2009 10:54:34 +0000 Peter Horton <phorton@bitbox.co.uk> wrote:
> Andrew Morton wrote: > > On Thu, 22 Oct 2009 15:22:28 +0100 > > phorton@bitbox.co.uk (Peter Horton) wrote: > > > >> To: ecashin@coraid.com > > > > Have you heard back from Ed on this? > > > > No. > > >> Cc: linux-kernel@vger.kernel.org > >> Subject: [PATCH] prevent AoE causing cache aliases > >> Date: Thu, 22 Oct 2009 15:22:28 +0100 > >> Sender: linux-kernel-owner@vger.kernel.org > >> User-Agent: Mutt/1.5.9i > >> > >> This patch prevents the AoE block driver from creating cache aliases of > >> page cache pages on machines with virtually indexed caches. > >> > >> Building kernels on an AT91SAM9G20 board without this patch fails with > >> segmentation faults after a couple of passes. > >> > >> > >> Index: linux-2.6.31/drivers/block/aoe/aoecmd.c > >> =================================================================== > >> --- linux-2.6.31.orig/drivers/block/aoe/aoecmd.c 2009-09-09 23:13:59.000000000 +0100 > >> +++ linux-2.6.31/drivers/block/aoe/aoecmd.c 2009-10-22 10:24:50.000000000 +0100 > >> @@ -735,6 +735,21 @@ > >> part_stat_unlock(); > >> } > >> > >> +/* > >> + * Ensure we don't create aliases in VI caches > >> + */ > >> +static inline void > >> +killalias(struct bio *bio) > >> +{ > >> + struct bio_vec *bv; > >> + int i; > >> + > >> + if (bio_data_dir(bio) == READ) > >> + __bio_for_each_segment(bv, bio, i, 0) { > >> + flush_dcache_page(bv->bv_page); > >> + } > >> +} > >> + > >> void > >> aoecmd_ata_rsp(struct sk_buff *skb) > >> { > >> @@ -853,8 +868,12 @@ > >> > >> if (buf && --buf->nframesout == 0 && buf->resid == 0) { > >> diskstats(d->gd, buf->bio, jiffies - buf->stime, buf->sector); > >> - n = (buf->flags & BUFFL_FAIL) ? -EIO : 0; > >> - bio_endio(buf->bio, n); > >> + if (buf->flags & BUFFL_FAIL) > >> + bio_endio(buf->bio, -EIO); > >> + else { > >> + killalias(buf->bio); > >> + bio_endio(buf->bio, 0); > >> + } > >> mempool_free(buf, d->bufpool); > >> } > > > > Looks OK. > > > > This bugfix will cause a pointless __bio_for_each_segment() busywait > > loop to be executed on architectures for which flush_dcache_page() is a > > no-op. > > > > We don't have infrastructure to fix that. > > Couldn't we add a flag to the bio that users could set to indicate that > they are not house trained with respect to the D-cache (i.e non-DMA > drivers). Architectures that needed to could then flush the relevant > pages in the bio_endio() path somewhere. At the moment all the non-DMA > block drivers need to be aware of the cache aliasing issue which means > this problem keeps arising ... >
Could. We'll need to change each arch _somehow_. Even if it's a matter of adding `#define i_am_not_house_trained' to the troublesome ones or something, then ifdeffing existing code.
I was thinking that a general bio_flush_dcache_pages() in block core (or in each arch) would be a suitable way to handle this but I was unable to find other drivers which needed it after a brief search.
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