Messages in this thread Patch in this message | | | Date | Sun, 24 Aug 2008 14:48:22 +0900 | Subject | Re: Writable packet CD-RW mounting broken in 2.6.26 by your commit 68154e90c9d1492d570671ae181d9a8f8530da55 | From | FUJITA Tomonori <> |
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On Sat, 23 Aug 2008 22:48:55 +0100 Nix <nix@esperi.org.uk> wrote:
> On 8 Aug 2008, Alexey Dobriyan told this: > > > On Fri, Aug 08, 2008 at 07:14:37AM +0400, Alexey Dobriyan wrote: > >> On Wed, Aug 06, 2008 at 08:12:49PM +0100, Nix wrote: > >> > It seems to be impossible to mount packet-written CD-RWs writably in > >> > 2.6.26.x, even as root. Things worked in 2.6.25.x. > > Bisected. The bug starts here: > > commit 68154e90c9d1492d570671ae181d9a8f8530da55 > Author: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> > Date: Fri Apr 25 12:47:50 2008 +0200 > > block: add dma alignment and padding support to blk_rq_map_kern > > This patch adds bio_copy_kern similar to > bio_copy_user. blk_rq_map_kern uses bio_copy_kern instead of > bio_map_kern if necessary. > > bio_copy_kern uses temporary pages and the bi_end_io callback frees > these pages. bio_copy_kern saves the original kernel buffer at > bio->bi_private it doesn't use something like struct bio_map_data to > store the information about the caller. > > Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> > Cc: Tejun Heo <htejun@gmail.com> > Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Sorry about the bug and thanks for the investigation.
> So something in this patch seems to be corrupting the results of at > least some ATAPI sg requests going to or from the block layer: and > indeed blk_rq_map_kern(), called by pkt_generic_packet(), is changed by > this patch. > > Tomonori, Jens, can you see any immediate cause of this? It seems to me > that the alignment check in blk_rq_map_kern() *must* be going wrong, > somehow: this can't be an unaligned buffer or the code wouldn't have > worked before the patch, yet if the buffer was aligned, we should be > calling bio_map_kern(), which this patch hasn't changed. Perhaps the > buffer length of 12 is leading it to believe that it should go via a > bounce buffer and is calling the new code (and tripping some bug in it, > since presumably even the new code isn't expected to corrupt the data in > flight ;) )
Using bio_copy_kern() should be fine since it does the same thing that bio_map_kern() does (the difference is that bio_copy_kern() does extra memory copy).
Actually, pkt_probe_settings() should use bio_copy_kern because it tries to do DMA with a buffer on the stack (it doesn't work on some architectures). blk_rq_map_kern() in the latest git has the stack checking too.
I think that I put a bug in bio_copy_kern(). Can you try this patch?
I think that bio_uncopy_user has the same bug. I'll send a patch after fixing this bug.
diff --git a/fs/bio.c b/fs/bio.c index 8000e2f..f58a7ba 100644 --- a/fs/bio.c +++ b/fs/bio.c @@ -942,19 +942,22 @@ static void bio_copy_kern_endio(struct bio *bio, int err) { struct bio_vec *bvec; const int read = bio_data_dir(bio) == READ; - char *p = bio->bi_private; + struct bio_map_data *bmd = bio->bi_private; int i; + char *p = bmd->sgvecs[0].iov_base; __bio_for_each_segment(bvec, bio, i, 0) { char *addr = page_address(bvec->bv_page); + int len = bmd->iovecs[i].bv_len; if (read && !err) - memcpy(p, addr, bvec->bv_len); + memcpy(p, addr, len); __free_page(bvec->bv_page); - p += bvec->bv_len; + p += len; } + bio_free_map_data(bmd); bio_put(bio); } @@ -978,11 +981,21 @@ struct bio *bio_copy_kern(struct request_queue *q, void *data, unsigned int len, const int nr_pages = end - start; struct bio *bio; struct bio_vec *bvec; + struct bio_map_data *bmd; int i, ret; + struct sg_iovec iov; + + iov.iov_base = data; + iov.iov_len = len; + + bmd = bio_alloc_map_data(nr_pages, 1); + if (!bmd) + return ERR_PTR(-ENOMEM); + ret = -ENOMEM; bio = bio_alloc(gfp_mask, nr_pages); if (!bio) - return ERR_PTR(-ENOMEM); + goto out_bmd; while (len) { struct page *page; @@ -1016,14 +1029,18 @@ struct bio *bio_copy_kern(struct request_queue *q, void *data, unsigned int len, } } - bio->bi_private = data; + bio->bi_private = bmd; bio->bi_end_io = bio_copy_kern_endio; + + bio_set_map_data(bmd, bio, &iov, 1); return bio; cleanup: bio_for_each_segment(bvec, bio, i) __free_page(bvec->bv_page); bio_put(bio); +out_bmd: + bio_free_map_data(bmd); return ERR_PTR(ret); }
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