st: fix race in st_scsi_execute_end

commit c68bf8eeaa57c852e74adcf597237be149eef830 upstream.

The call to complete() in st_scsi_execute_end() wakes up sleeping thread
in write_behind_check(), which frees the st_request, thus invalidating
the pointer to the associated bio structure, which is then passed to the
blk_rq_unmap_user(). Fix by storing pointer to bio structure into
temporary local variable.

This bug is present since at least linux-2.6.32.

Signed-off-by: Petr Uzel <petr.uzel@suse.cz>
Reported-by: Juergen Groß <juergen.gross@ts.fujitsu.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Kai Mäkisara <kai.makisara@kolumbus.fi>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index 5081f97cbdaa2ac26e5ef5d873ac8841f8e81d88..723da1d14e8304a95e6cd4114132c2e8c82cc8f6 100644 (file)
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -461,14 +461,16 @@ static void st_scsi_execute_end(struct request *req, int uptodate)
 {
        struct st_request *SRpnt = req->end_io_data;
        struct scsi_tape *STp = SRpnt->stp;
+       struct bio *tmp;
 
        STp->buffer->cmdstat.midlevel_result = SRpnt->result = req->errors;
        STp->buffer->cmdstat.residual = req->resid_len;
 
+       tmp = SRpnt->bio;
        if (SRpnt->waiting)
                complete(SRpnt->waiting);
 
-       blk_rq_unmap_user(SRpnt->bio);
+       blk_rq_unmap_user(tmp);
        __blk_put_request(req->q, req);
 }