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| author |   Ming Lei <ming.lei@redhat.com> | 2025-07-16 19:48:08 +0800 |
|---|---|---|
| committer |   Jens Axboe <axboe@kernel.dk> | 2025-07-16 06:33:44 -0600 |
| commit | c4706c5058a7bd7d7c20f3b24a8f523ecad44e83 (patch) | |
| tree | cbc6a83e6938f20b2588c3d471671510936daf2d | |
| parent | block: fix kobject leak in blk_unregister_queue (diff) | |
| download | wireguard-linux-c4706c5058a7bd7d7c20f3b24a8f523ecad44e83.tar.xz wireguard-linux-c4706c5058a7bd7d7c20f3b24a8f523ecad44e83.zip | |
loop: use kiocb helpers to fix lockdep warning
The lockdep tool can report a circular lock dependency warning in the loop
driver's AIO read/write path:
```
[ 6540.587728] kworker/u96:5/72779 is trying to acquire lock:
[ 6540.593856] ff110001b5968440 (sb_writers#9){.+.+}-{0:0}, at: loop_process_work+0x11a/0xf70 [loop]
[ 6540.603786]
[ 6540.603786] but task is already holding lock:
[ 6540.610291] ff110001b5968440 (sb_writers#9){.+.+}-{0:0}, at: loop_process_work+0x11a/0xf70 [loop]
[ 6540.620210]
[ 6540.620210] other info that might help us debug this:
[ 6540.627499] Possible unsafe locking scenario:
[ 6540.627499]
[ 6540.634110] CPU0
[ 6540.636841] ----
[ 6540.639574] lock(sb_writers#9);
[ 6540.643281] lock(sb_writers#9);
[ 6540.646988]
[ 6540.646988] *** DEADLOCK ***
```
This patch fixes the issue by using the AIO-specific helpers
`kiocb_start_write()` and `kiocb_end_write()`. These functions are
designed to be used with a `kiocb` and manage write sequencing
correctly for asynchronous I/O without introducing the problematic
lock dependency.
The `kiocb` is already part of the `loop_cmd` struct, so this change
also simplifies the completion function `lo_rw_aio_do_completion()` by
using the `iocb` from the `cmd` struct directly, instead of retrieving
the loop device from the request queue.
Fixes: 39d86db34e41 ("loop: add file_start_write() and file_end_write()")
Cc: Changhui Zhong <czhong@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250716114808.3159657-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
| -rw-r--r-- | drivers/block/loop.c | 5 |
1 files changed, 2 insertions, 3 deletions
diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 500840e4a74e..8d994cae3b83 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -308,14 +308,13 @@ end_io: static void lo_rw_aio_do_completion(struct loop_cmd *cmd) { struct request *rq = blk_mq_rq_from_pdu(cmd); - struct loop_device *lo = rq->q->queuedata; if (!atomic_dec_and_test(&cmd->ref)) return; kfree(cmd->bvec); cmd->bvec = NULL; if (req_op(rq) == REQ_OP_WRITE) - file_end_write(lo->lo_backing_file); + kiocb_end_write(&cmd->iocb); if (likely(!blk_should_fake_timeout(rq->q))) blk_mq_complete_request(rq); } @@ -391,7 +390,7 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, } if (rw == ITER_SOURCE) { - file_start_write(lo->lo_backing_file); + kiocb_start_write(&cmd->iocb); ret = file->f_op->write_iter(&cmd->iocb, &iter); } else ret = file->f_op->read_iter(&cmd->iocb, &iter); |