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Fix zvol+btrfs hang 

When using a zvol to back a btrfs filesystem the btrfs mount
would hang.  This was due to the bio completion callback used
in btrfs assuming that lower level drivers would never modify
the bio->bi_io_vecs after they were submitted via bio_submit().
If they are modified btrfs will miscalculate which pages need
to be unlocked resulting in a hang.

It's worth mentioning that other file systems such as ext[234]
and xfs work fine because they do not make the same assumption
in the bio completion callback.

The most straight forward way to fix the issue is to present
the semantics expected by btrfs.  This is done by cloning the
bios attached to each request and then using the clones bvecs
to perform the required accounting.  The clones are freed after
each read/write and the original unmodified bios are linked back
in to the request.

Signed-off-by: Chris Wedgwood <cw@f00f.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #469
This commit is contained in:
Brian Behlendorf 2012-11-08 14:18:22 -08:00
parent bbf8c74805
commit e26ade5101
1 changed files with 77 additions and 0 deletions
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77
module/zfs/dmu.c
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@ -1022,11 +1022,57 @@ dmu_req_copy(void *arg_buf, int size, int *offset, struct request *req)
return 0;
}
static void
dmu_bio_put(struct bio *bio)
{
struct bio *bio_next;
while (bio) {
bio_next = bio->bi_next;
bio_put(bio);
bio = bio_next;
}
}
static int
dmu_bio_clone(struct bio *bio, struct bio **bio_copy)
{
struct bio *bio_root = NULL;
struct bio *bio_last = NULL;
struct bio *bio_new;
if (bio == NULL)
return EINVAL;
while (bio) {
bio_new = bio_clone(bio, GFP_NOIO);
if (bio_new == NULL) {
dmu_bio_put(bio_root);
return ENOMEM;
}
if (bio_last) {
bio_last->bi_next = bio_new;
bio_last = bio_new;
} else {
bio_root = bio_new;
bio_last = bio_new;
}
bio = bio->bi_next;
}
*bio_copy = bio_root;
return 0;
}
int
dmu_read_req(objset_t *os, uint64_t object, struct request *req)
{
uint64_t size = blk_rq_bytes(req);
uint64_t offset = blk_rq_pos(req) << 9;
struct bio *bio_saved = req->bio;
dmu_buf_t **dbp;
int numbufs, i, err;
@ -1039,6 +1085,17 @@ dmu_read_req(objset_t *os, uint64_t object, struct request *req)
if (err)
return (err);
/*
* Clone the bio list so the bv->bv_offset and bv->bv_len members
* can be safely modified. The original bio list is relinked in to
* the request when the function exits. This is required because
* some file systems blindly assume that these values will remain
* constant between bio_submit() and the IO completion callback.
*/
err = dmu_bio_clone(bio_saved, &req->bio);
if (err)
goto error;
for (i = 0; i < numbufs; i++) {
int tocpy, didcpy, bufoff;
dmu_buf_t *db = dbp[i];
@ -1062,6 +1119,10 @@ dmu_read_req(objset_t *os, uint64_t object, struct request *req)
offset += didcpy;
err = 0;
}
dmu_bio_put(req->bio);
req->bio = bio_saved;
error:
dmu_buf_rele_array(dbp, numbufs, FTAG);
return (err);
@ -1072,6 +1133,7 @@ dmu_write_req(objset_t *os, uint64_t object, struct request *req, dmu_tx_t *tx)
{
uint64_t size = blk_rq_bytes(req);
uint64_t offset = blk_rq_pos(req) << 9;
struct bio *bio_saved = req->bio;
dmu_buf_t **dbp;
int numbufs;
int err = 0;
@ -1085,6 +1147,17 @@ dmu_write_req(objset_t *os, uint64_t object, struct request *req, dmu_tx_t *tx)
if (err)
return (err);
/*
* Clone the bio list so the bv->bv_offset and bv->bv_len members
* can be safely modified. The original bio list is relinked in to
* the request when the function exits. This is required because
* some file systems blindly assume that these values will remain
* constant between bio_submit() and the IO completion callback.
*/
err = dmu_bio_clone(bio_saved, &req->bio);
if (err)
goto error;
for (i = 0; i < numbufs; i++) {
int tocpy, didcpy, bufoff;
dmu_buf_t *db = dbp[i];
@ -1119,7 +1192,11 @@ dmu_write_req(objset_t *os, uint64_t object, struct request *req, dmu_tx_t *tx)
err = 0;
}
dmu_bio_put(req->bio);
req->bio = bio_saved;
error:
dmu_buf_rele_array(dbp, numbufs, FTAG);
return (err);
}