block,scsi: fixup blk_get_request dead queue scenarios

The blk_get_request function may fail in low-memory conditions or during
device removal (even if __GFP_WAIT is set). To distinguish between these
errors, modify the blk_get_request call stack to return the appropriate
ERR_PTR. Verify that all callers check the return status and consider
IS_ERR instead of a simple NULL pointer check.

For consistency, make a similar change to the blk_mq_alloc_request leg
of blk_get_request.  It may fail if the queue is dead, or the caller was
unwilling to wait.

Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>
Acked-by: Jiri Kosina <jkosina@suse.cz> [for pktdvd]
Acked-by: Boaz Harrosh <bharrosh@panasas.com> [for osd]
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/block/bsg.c b/block/bsg.c
index ff46addde5d8..73c78fd12cc1 100644
--- a/block/bsg.c
+++ b/block/bsg.c
@@ -270,8 +270,8 @@ bsg_map_hdr(struct bsg_device *bd, struct sg_io_v4 *hdr, fmode_t has_write_perm,
          * map scatter-gather elements separately and string them to request
          */
         rq = blk_get_request(q, rw, GFP_KERNEL);
-        if (!rq)
-                return ERR_PTR(-ENOMEM);
+        if (IS_ERR(rq))
+                return rq;
         blk_rq_set_block_pc(rq);
 
         ret = blk_fill_sgv4_hdr_rq(q, rq, hdr, bd, has_write_perm);
@@ -285,8 +285,8 @@ bsg_map_hdr(struct bsg_device *bd, struct sg_io_v4 *hdr, fmode_t has_write_perm,
                 }
 
                 next_rq = blk_get_request(q, READ, GFP_KERNEL);
-                if (!next_rq) {
-                        ret = -ENOMEM;
+                if (IS_ERR(next_rq)) {
+                        ret = PTR_ERR(next_rq);
                         goto out;
                 }
                 rq->next_rq = next_rq;