From: Jiri Kosina jkosina@suse.cz
commit 263c61581a38d0a5ad1f5f4a9143b27d68caeffd upstream.
Since the switch of floppy driver to blk-mq, the contended (fdc_busy) case in floppy_queue_rq() is not handled correctly.
In case we reach floppy_queue_rq() with fdc_busy set (i.e. with the floppy locked due to another request still being in-flight), we put the request on the list of requests and return BLK_STS_OK to the block core, without actually scheduling delayed work / doing further processing of the request. This means that processing of this request is postponed until another request comes and passess uncontended.
Which in some cases might actually never happen and we keep waiting indefinitely. The simple testcase is
for i in `seq 1 2000`; do echo -en $i '\r'; blkid --info /dev/fd0 2> /dev/null; done
run in quemu. That reliably causes blkid eventually indefinitely hanging in __floppy_read_block_0() waiting for completion, as the BIO callback never happens, and no further IO is ever submitted on the (non-existent) floppy device. This was observed reliably on qemu-emulated device.
Fix that by not queuing the request in the contended case, and return BLK_STS_RESOURCE instead, so that blk core handles the request rescheduling and let it pass properly non-contended later.
Fixes: a9f38e1dec107a ("floppy: convert to blk-mq") Cc: stable@vger.kernel.org Tested-by: Libor Pechacek lpechacek@suse.cz Signed-off-by: Jiri Kosina jkosina@suse.cz Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/block/floppy.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
--- a/drivers/block/floppy.c +++ b/drivers/block/floppy.c @@ -2938,17 +2938,17 @@ static blk_status_t floppy_queue_rq(stru (unsigned long long) current_req->cmd_flags)) return BLK_STS_IOERR;
- spin_lock_irq(&floppy_lock); - list_add_tail(&bd->rq->queuelist, &floppy_reqs); - spin_unlock_irq(&floppy_lock); - if (test_and_set_bit(0, &fdc_busy)) { /* fdc busy, this new request will be treated when the current one is done */ is_alive(__func__, "old request running"); - return BLK_STS_OK; + return BLK_STS_RESOURCE; }
+ spin_lock_irq(&floppy_lock); + list_add_tail(&bd->rq->queuelist, &floppy_reqs); + spin_unlock_irq(&floppy_lock); + command_status = FD_COMMAND_NONE; __reschedule_timeout(MAXTIMEOUT, "fd_request"); set_fdc(0);