Messages in this thread | | | Date | Wed, 04 Nov 2009 10:54:34 +0000 | From | Peter Horton <> | Subject | Re: [PATCH] prevent AoE causing cache aliases |
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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 ...
P.
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