[PATCH] ide: Workaround PM problem

The logic in ide_do_request() doesn't guarantee that both drives will be
serviced after a call.  It may "forget" to service one in some
circumstances, including when one of the drive is suspended (it will
eventually fail to service the slave when the master is suspended for
example).  This prevents the wakeup requests that gets queued on wakeup
from sleep from beeing serviced in some cases when 2 drives are sharing
an IDE bus.

The problem is deep enough in the way this code works (and there are
probably a few other problematic but rare corner cases) and fixing it
would require some major rethinking of the way IDE decides which channel
to service.  This is not 2.6.14 material.  However, in the meantime,
Bart has accepted this simple workaround that will fix the crash on
wakeup from sleep since this specific corner case is actually hitting
users to get into 2.6.14.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/drivers/ide/ide-io.c b/drivers/ide/ide-io.c
index 9e9cf1407311f92eabc53cf702913f70537b6c17..5275cbb1afe9c790fe9b427c0c916dcfa7c4b9a3 100644 (file)
--- a/drivers/ide/ide-io.c
+++ b/drivers/ide/ide-io.c
@@ -1101,6 +1101,7 @@ static void ide_do_request (ide_hwgroup_t *hwgroup, int masked_irq)
        ide_hwif_t      *hwif;
        struct request  *rq;
        ide_startstop_t startstop;
+       int             loops = 0;
 
        /* for atari only: POSSIBLY BROKEN HERE(?) */
        ide_get_lock(ide_intr, hwgroup);
@@ -1153,6 +1154,7 @@ static void ide_do_request (ide_hwgroup_t *hwgroup, int masked_irq)
                        /* no more work for this hwgroup (for now) */
                        return;
                }
+       again:
                hwif = HWIF(drive);
                if (hwgroup->hwif->sharing_irq &&
                    hwif != hwgroup->hwif &&
@@ -1192,8 +1194,14 @@ static void ide_do_request (ide_hwgroup_t *hwgroup, int masked_irq)
                 * though. I hope that doesn't happen too much, hopefully not
                 * unless the subdriver triggers such a thing in its own PM
                 * state machine.
+                *
+                * We count how many times we loop here to make sure we service
+                * all drives in the hwgroup without looping for ever
                 */
                if (drive->blocked && !blk_pm_request(rq) && !(rq->flags & REQ_PREEMPT)) {
+                       drive = drive->next ? drive->next : hwgroup->drive;
+                       if (loops++ < 4 && !blk_queue_plugged(drive->queue))
+                               goto again;
                        /* We clear busy, there should be no pending ATA command at this point. */
                        hwgroup->busy = 0;
                        break;