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    SubjectRe: 4.15.14 crash with iscsi target and dvd
    On Mon, Apr 09, 2018 at 09:30:11PM +0000, Bart Van Assche wrote:
    > On Sun, 2018-04-08 at 12:02 -0400, Wakko Warner wrote:
    > > I finished with git bisect. Here's the output:
    > > 84c8590646d5b35804bac60eb58b145839b5893e is the first bad commit
    > > commit 84c8590646d5b35804bac60eb58b145839b5893e
    > > Author: Ming Lei <tom.leiming@gmail.com>
    > > Date: Fri Nov 11 20:05:32 2016 +0800
    > >
    > > target: avoid accessing .bi_vcnt directly
    > >
    > > When the bio is full, bio_add_pc_page() will return zero,
    > > so use this information tell when the bio is full.
    > >
    > > Also replace access to .bi_vcnt for pr_debug() with bio_segments().
    > >
    > > Reviewed-by: Christoph Hellwig <hch@lst.de>
    > > Signed-off-by: Ming Lei <tom.leiming@gmail.com>
    > > Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
    > > Signed-off-by: Jens Axboe <axboe@fb.com>
    > >
    > > :040000 040000 a3ebbb71c52ee4eb8c3be4d033b81179211bf704 de39a328dbd1b18519946b3ad46d9302886e0dd0 M drivers
    > >
    > > I did a diff between HEAD^ and HEAD and manually patched the file from
    > > 4.15.14. It's not an exact revert. I'm running it now and it's working.
    > > I'll do a better test later on. Here's the patch:
    > >
    > > --- a/drivers/target/target_core_pscsi.c 2018-02-04 14:31:31.077316617 -0500
    > > +++ b/drivers/target/target_core_pscsi.c 2018-04-08 11:43:49.588641374 -0400
    > > @@ -915,7 +915,9 @@
    > > bio, page, bytes, off);
    > > pr_debug("PSCSI: bio->bi_vcnt: %d nr_vecs: %d\n",
    > > bio_segments(bio), nr_vecs);
    > > - if (rc != bytes) {
    > > + if (rc != bytes)
    > > + goto fail;
    > > + if (bio->bi_vcnt > nr_vecs) {
    > > pr_debug("PSCSI: Reached bio->bi_vcnt max:"
    > > " %d i: %d bio: %p, allocating another"
    > > " bio\n", bio->bi_vcnt, i, bio);
    >
    > Hello Ming,
    >
    > Can you have a look at this? The start of this e-mail thread is available at
    > https://www.mail-archive.com/linux-scsi@vger.kernel.org/msg72574.html.

    Sure, thanks for your sharing.

    Wakko, could you test the following patch and see if there is any
    difference?

    --
    diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
    index 0d99b242e82e..6147178f1f37 100644
    --- a/drivers/target/target_core_pscsi.c
    +++ b/drivers/target/target_core_pscsi.c
    @@ -888,7 +888,7 @@ pscsi_map_sg(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
    if (len > 0 && data_len > 0) {
    bytes = min_t(unsigned int, len, PAGE_SIZE - off);
    bytes = min(bytes, data_len);
    -
    + new_bio:
    if (!bio) {
    nr_vecs = min_t(int, BIO_MAX_PAGES, nr_pages);
    nr_pages -= nr_vecs;
    @@ -931,6 +931,7 @@ pscsi_map_sg(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
    * be allocated with pscsi_get_bio() above.
    */
    bio = NULL;
    + goto new_bio;
    }

    data_len -= bytes;
    --
    Ming

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