On 12/08/2017 08:38 AM, Michele Ballabio wrote:

quoted

Hi,
	kernels 4.13.*, 4.14.* 4.15-rc2 crash on occasion, especially
on x86-32 systems. To trigger the problem, run as root:

while true
do
        /sbin/udevadm trigger --type=subsystems --action=change
        /sbin/udevadm trigger --type=devices --action=change
        /sbin/udevadm settle --timeout=120
done

(Thanks to Patrick Volkerding for the reproducer).

Sometimes the kernel oopses immediately, sometimes a bit later (less than
five minutes).

The bisection pointed to commit caa4b02476e31fc7933d2138062f7f355d3cd8f7
(blk-map: call blk_queue_bounce from blk_rq_append_bio). A revert
fixes the problem (tested on 4.13 and master).

Thanks for your report - can you try the below patch? Totally
untested...

diff --git a/block/blk-map.c b/block/blk-map.c
index b21f8e86f120..ad970719a1fc 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c

@@ -12,22 +12,22 @@
 #include "blk.h"
 
 /*
- * Append a bio to a passthrough request.  Only works can be merged into
- * the request based on the driver constraints.
+ * Append a bio to a passthrough request.  Only works if the bio can be merged
+ * into the request based on the driver constraints.
  */
-int blk_rq_append_bio(struct request *rq, struct bio *bio)
+int blk_rq_append_bio(struct request *rq, struct bio **bio)
 {
-	blk_queue_bounce(rq->q, &bio);
+	blk_queue_bounce(rq->q, bio);
 
 	if (!rq->bio) {
-		blk_rq_bio_prep(rq->q, rq, bio);
+		blk_rq_bio_prep(rq->q, rq, *bio);
 	} else {
-		if (!ll_back_merge_fn(rq->q, rq, bio))
+		if (!ll_back_merge_fn(rq->q, rq, *bio))
 			return -EINVAL;
 
-		rq->biotail->bi_next = bio;
-		rq->biotail = bio;
-		rq->__data_len += bio->bi_iter.bi_size;
+		rq->biotail->bi_next = *bio;
+		rq->biotail = *bio;
+		rq->__data_len += (*bio)->bi_iter.bi_size;
 	}
 
 	return 0;

@@ -73,8 +73,9 @@ static int __blk_rq_map_user_iov(struct request *rq,
 	 * We link the bounce buffer in and could have to traverse it
 	 * later so we have to get a ref to prevent it from being freed
 	 */
-	ret = blk_rq_append_bio(rq, bio);
 	bio_get(bio);
+
+	ret = blk_rq_append_bio(rq, &bio);
 	if (ret) {
 		bio_endio(bio);
 		__blk_rq_unmap_user(orig_bio);

@@ -236,7 +237,7 @@ int blk_rq_map_kern(struct request_queue *q, struct request *rq, void *kbuf,
 	if (do_copy)
 		rq->rq_flags |= RQF_COPY_USER;
 
-	ret = blk_rq_append_bio(rq, bio);
+	ret = blk_rq_append_bio(rq, &bio);
 	if (unlikely(ret)) {
 		/* request is too big */
 		bio_put(bio);

diff --git a/drivers/scsi/osd/osd_initiator.c b/drivers/scsi/osd/osd_initiator.c
index a4f28b7e4c65..e18877177f1b 100644
--- a/drivers/scsi/osd/osd_initiator.c
+++ b/drivers/scsi/osd/osd_initiator.c

@@ -1576,7 +1576,9 @@ static struct request *_make_request(struct request_queue *q, bool has_write,
 		return req;
 
 	for_each_bio(bio) {
-		ret = blk_rq_append_bio(req, bio);
+		struct bio *bounce_bio = bio;
+
+		ret = blk_rq_append_bio(req, &bounce_bio);
 		if (ret)
 			return ERR_PTR(ret);
 	}

diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
index 7c69b4a9694d..0d99b242e82e 100644
--- a/drivers/target/target_core_pscsi.c
+++ b/drivers/target/target_core_pscsi.c

@@ -920,7 +920,7 @@ pscsi_map_sg(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
 					" %d i: %d bio: %p, allocating another"
 					" bio\n", bio->bi_vcnt, i, bio);
 
-				rc = blk_rq_append_bio(req, bio);
+				rc = blk_rq_append_bio(req, &bio);
 				if (rc) {
 					pr_err("pSCSI: failed to append bio\n");
 					goto fail;

@@ -938,7 +938,7 @@ pscsi_map_sg(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
 	}
 
 	if (bio) {
-		rc = blk_rq_append_bio(req, bio);
+		rc = blk_rq_append_bio(req, &bio);
 		if (rc) {
 			pr_err("pSCSI: failed to append bio\n");
 			goto fail;

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 8089ca17db9a..06b88d38f611 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h

@@ -948,7 +948,7 @@ extern int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
 extern void blk_rq_unprep_clone(struct request *rq);
 extern blk_status_t blk_insert_cloned_request(struct request_queue *q,
 				     struct request *rq);
-extern int blk_rq_append_bio(struct request *rq, struct bio *bio);
+extern int blk_rq_append_bio(struct request *rq, struct bio **bio);
 extern void blk_delay_queue(struct request_queue *, unsigned long);
 extern void blk_queue_split(struct request_queue *, struct bio **);
 extern void blk_recount_segments(struct request_queue *, struct bio *);