From: Bart Van Assche bvanassche@acm.org
[ Upstream commit 96d86e6a80a3ab9aff81d12f9f1f2a0da2917d38 ]
RQF_PREEMPT is used for two different purposes in the legacy IDE code:
1. To mark power management requests.
2. To mark requests that should preempt another request. An (old) explanation of that feature is as follows: "The IDE driver in the Linux kernel normally uses a series of busywait delays during its initialization. When the driver executes these busywaits, the kernel does nothing for the duration of the wait. The time spent in these waits could be used for other initialization activities, if they could be run concurrently with these waits.
More specifically, busywait-style delays such as udelay() in module init functions inhibit kernel preemption because the Big Kernel Lock is held, while yielding APIs such as schedule_timeout() allow preemption. This is true because the kernel handles the BKL specially and releases and reacquires it across reschedules allowed by the current thread.
This IDE-preempt specification requires that the driver eliminate these busywaits and replace them with a mechanism that allows other work to proceed while the IDE driver is initializing."
Since I haven't found an implementation of (2), do not set the PREEMPT flag for sense requests. This patch causes sense requests to be postponed while a drive is suspended instead of being submitted to ide_queue_rq().
If it would ever be necessary to restore the IDE PREEMPT functionality, that can be done by introducing a new flag in struct ide_request.
Link: https://lore.kernel.org/r/20201209052951.16136-4-bvanassche@acm.org Cc: David S. Miller davem@davemloft.net Cc: Alan Stern stern@rowland.harvard.edu Cc: Can Guo cang@codeaurora.org Cc: Stanley Chu stanley.chu@mediatek.com Cc: Ming Lei ming.lei@redhat.com Cc: Rafael J. Wysocki rafael.j.wysocki@intel.com Reviewed-by: Christoph Hellwig hch@lst.de Reviewed-by: Hannes Reinecke hare@suse.de Reviewed-by: Jens Axboe axboe@kernel.dk Signed-off-by: Bart Van Assche bvanassche@acm.org Signed-off-by: Martin K. Petersen martin.petersen@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/ide/ide-atapi.c | 1 - drivers/ide/ide-io.c | 5 ----- 2 files changed, 6 deletions(-)
diff --git a/drivers/ide/ide-atapi.c b/drivers/ide/ide-atapi.c index 8b2b72b93885..4224c4dd8963 100644 --- a/drivers/ide/ide-atapi.c +++ b/drivers/ide/ide-atapi.c @@ -213,7 +213,6 @@ void ide_prep_sense(ide_drive_t *drive, struct request *rq) sense_rq->rq_disk = rq->rq_disk; sense_rq->cmd_flags = REQ_OP_DRV_IN; ide_req(sense_rq)->type = ATA_PRIV_SENSE; - sense_rq->rq_flags |= RQF_PREEMPT;
req->cmd[0] = GPCMD_REQUEST_SENSE; req->cmd[4] = cmd_len; diff --git a/drivers/ide/ide-io.c b/drivers/ide/ide-io.c index 0d93e0cfbeaf..438176084610 100644 --- a/drivers/ide/ide-io.c +++ b/drivers/ide/ide-io.c @@ -527,11 +527,6 @@ void do_ide_request(struct request_queue *q) * above to return us whatever is in the queue. Since we call * ide_do_request() ourselves, we end up taking requests while * the queue is blocked... - * - * We let requests forced at head of queue with ide-preempt - * though. I hope that doesn't happen too much, hopefully not - * unless the subdriver triggers such a thing in its own PM - * state machine. */ if ((drive->dev_flags & IDE_DFLAG_BLOCKED) && ata_pm_request(rq) == 0 &&