| Message ID | 20240711133652.589770-1-f.ebner@proxmox.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block/copy-before-write: wait for conflicts when read locking to avoid assertion failure | expand |
On 11.07.24 16:36, Fiona Ebner wrote: > There is no protection against two callers of cbw_snapshot_read_lock() > calling reqlist_init_req() with overlapping ranges, and > reqlist_init_req() asserts that there are no conflicting requests. > > In particular, two cbw_co_snapshot_block_status() callers can race, > with the second calling reqlist_init_req() before the first one > finishes and removes its conflicting request, leading to an assertion > failure. > > Reproducer script [0] and backtrace [1] are attached below. Understand. But seems in case of CBW read-lock, nothing bad in intersecting read requests? reqlist is shared with backup, where we care to avoid intersecting requests in the list. What about just move the assertion to block_copy_task_create() ? And add comment somewhere that we support intersecting reads in frozen_read_reqs. > > [0]: > >> #!/bin/bash -e >> dd if=/dev/urandom of=/tmp/disk.raw bs=1M count=1024 >> ./qemu-img create /tmp/fleecing.raw -f raw 1G >> ( >> ./qemu-system-x86_64 --qmp stdio \ >> --blockdev raw,node-name=node0,file.driver=file,file.filename=/tmp/disk.raw \ >> --blockdev raw,node-name=node1,file.driver=file,file.filename=/tmp/fleecing.raw \ >> <<EOF >> {"execute": "qmp_capabilities"} >> {"execute": "blockdev-add", "arguments": { "driver": "copy-before-write", "file": "node0", "target": "node1", "node-name": "node3" } } >> {"execute": "blockdev-add", "arguments": { "driver": "snapshot-access", "file": "node3", "node-name": "snap0" } } >> {"execute": "nbd-server-start", "arguments": {"addr": { "type": "unix", "data": { "path": "/tmp/nbd.socket" } } } } >> {"execute": "block-export-add", "arguments": {"id": "exp0", "node-name": "snap0", "type": "nbd", "name": "exp0"}} >> EOF >> ) & >> sleep 5 >> while true; do >> ./qemu-nbd -d /dev/nbd0 >> ./qemu-nbd -c /dev/nbd0 nbd:unix:/tmp/nbd.socket:exportname=exp0 -f raw -r >> nbdinfo --map 'nbd+unix:///exp0?socket=/tmp/nbd.socket' >> done > > [1]: > >> #5 0x000071e5f0088eb2 in __GI___assert_fail (...) at ./assert/assert.c:101 >> #6 0x0000615285438017 in reqlist_init_req (...) at ../block/reqlist.c:23 >> #7 0x00006152853e2d98 in cbw_snapshot_read_lock (...) at ../block/copy-before-write.c:237 >> #8 0x00006152853e3068 in cbw_co_snapshot_block_status (...) at ../block/copy-before-write.c:304 >> #9 0x00006152853f4d22 in bdrv_co_snapshot_block_status (...) at ../block/io.c:3726 >> #10 0x000061528543a63e in snapshot_access_co_block_status (...) at ../block/snapshot-access.c:48 >> #11 0x00006152853f1a0a in bdrv_co_do_block_status (...) at ../block/io.c:2474 >> #12 0x00006152853f2016 in bdrv_co_common_block_status_above (...) at ../block/io.c:2652 >> #13 0x00006152853f22cf in bdrv_co_block_status_above (...) at ../block/io.c:2732 >> #14 0x00006152853d9a86 in blk_co_block_status_above (...) at ../block/block-backend.c:1473 >> #15 0x000061528538da6c in blockstatus_to_extents (...) at ../nbd/server.c:2374 >> #16 0x000061528538deb1 in nbd_co_send_block_status (...) at ../nbd/server.c:2481 >> #17 0x000061528538f424 in nbd_handle_request (...) at ../nbd/server.c:2978 >> #18 0x000061528538f906 in nbd_trip (...) at ../nbd/server.c:3121 >> #19 0x00006152855a7caf in coroutine_trampoline (...) at ../util/coroutine-ucontext.c:175 > > Signed-off-by: Fiona Ebner <f.ebner@proxmox.com> > --- > block/copy-before-write.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/block/copy-before-write.c b/block/copy-before-write.c > index 853e01a1eb..376ff3f3e1 100644 > --- a/block/copy-before-write.c > +++ b/block/copy-before-write.c > @@ -234,6 +234,7 @@ cbw_snapshot_read_lock(BlockDriverState *bs, int64_t offset, int64_t bytes, > *req = (BlockReq) {.offset = -1, .bytes = -1}; > *file = s->target; > } else { > + reqlist_wait_all(&s->frozen_read_reqs, offset, bytes, &s->lock); > reqlist_init_req(&s->frozen_read_reqs, req, offset, bytes); > *file = bs->file; > }
diff --git a/block/copy-before-write.c b/block/copy-before-write.c index 853e01a1eb..376ff3f3e1 100644 --- a/block/copy-before-write.c +++ b/block/copy-before-write.c @@ -234,6 +234,7 @@ cbw_snapshot_read_lock(BlockDriverState *bs, int64_t offset, int64_t bytes, *req = (BlockReq) {.offset = -1, .bytes = -1}; *file = s->target; } else { + reqlist_wait_all(&s->frozen_read_reqs, offset, bytes, &s->lock); reqlist_init_req(&s->frozen_read_reqs, req, offset, bytes); *file = bs->file; }