| Message ID | nycvar.YFH.7.76.2005261146420.25812@cbobk.fhfr.pm (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block/floppy: fix contended case in floppy_queue_rq() | expand |
[ forgot to CC Omar, fixing ] On Tue, 26 May 2020, Jiri Kosina wrote: > From: Jiri Kosina <jkosina@suse.cz> > > 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> > --- > drivers/block/floppy.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c > index c3daa64cb52c..975cd0a6baa1 100644 > --- a/drivers/block/floppy.c > +++ b/drivers/block/floppy.c > @@ -2938,17 +2938,17 @@ static blk_status_t floppy_queue_rq(struct blk_mq_hw_ctx *hctx, > (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); > > -- > Jiri Kosina > SUSE Labs > >
On 5/26/20 3:49 AM, Jiri Kosina wrote: > From: Jiri Kosina <jkosina@suse.cz> > > 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. Applied, thanks.
diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c index c3daa64cb52c..975cd0a6baa1 100644 --- a/drivers/block/floppy.c +++ b/drivers/block/floppy.c @@ -2938,17 +2938,17 @@ static blk_status_t floppy_queue_rq(struct blk_mq_hw_ctx *hctx, (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);