ide: fix locking for manual DMA enable/disable ("hdparm -d")

Since hwif->ide_dma_check and hwif->ide_dma_on never queue any commands
(ide_config_drive_speed() sets transfer mode using polling and has no error
recovery) we are safe with setting hwgroup->busy for the time while DMA
setting for a drive is changed (so it won't race against I/O commands in fly).

I audited briefly all ->ide_dma_check/->ide_dma_on/->tuneproc/->speedproc
implementations and they all look OK wrt to this change.

This patch finally allowed me to close kernel bugzilla bug #8169
(once again thanks to Patrick Horn for reporting the issue & testing patches).

Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

1 files changed, 30 insertions, 7 deletions

diff --git a/drivers/ide/ide.c b/drivers/ide/ide.c
index 695610f0e3e4..a6f098fda884 100644
--- a/drivers/ide/ide.c
+++ b/drivers/ide/ide.c
@@ -1124,17 +1124,40 @@ static int set_io_32bit(ide_drive_t *drive, int arg)
 static int set_using_dma (ide_drive_t *drive, int arg)
 {
 #ifdef CONFIG_BLK_DEV_IDEDMA
+        ide_hwif_t *hwif = drive->hwif;
+        int err = -EPERM;
+
         if (!drive->id || !(drive->id->capability & 1))
-                return -EPERM;
-        if (HWIF(drive)->ide_dma_check == NULL)
-                return -EPERM;
+                goto out;
+
+        if (hwif->ide_dma_check == NULL)
+                goto out;
+
+        err = -EBUSY;
+        if (ide_spin_wait_hwgroup(drive))
+                goto out;
+        /*
+         * set ->busy flag, unlock and let it ride
+         */
+        hwif->hwgroup->busy = 1;
+        spin_unlock_irq(&ide_lock);
+
+        err = 0;
+
         if (arg) {
-                if (ide_set_dma(drive))
-                        return -EIO;
-                if (HWIF(drive)->ide_dma_on(drive)) return -EIO;
+                if (ide_set_dma(drive) || hwif->ide_dma_on(drive))
+                        err = -EIO;
         } else
                 ide_dma_off(drive);
-        return 0;
+
+        /*
+         * lock, clear ->busy flag and unlock before leaving
+         */
+        spin_lock_irq(&ide_lock);
+        hwif->hwgroup->busy = 0;
+        spin_unlock_irq(&ide_lock);
+out:
+        return err;
 #else
         return -EPERM;
 #endif