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authorNeilBrown <neilb@suse.de>2013-08-27 16:44:13 +1000
committerNeilBrown <neilb@suse.de>2013-08-27 16:45:00 +1000
commit260fa034ef7a4ff8b73068b48ac497edd5217491 (patch)
tree6a328502545c8f155b34c08c72f7023166991bce
parent7a0a5355cbc71efa430c3730ffbd67ae04abfe31 (diff)
downloadlinux-260fa034ef7a4ff8b73068b48ac497edd5217491.tar.bz2
md: avoid deadlock when dirty buffers during md_stop.
When the last process closes /dev/mdX sync_blockdev will be called so that all buffers get flushed. So if it is then opened for the STOP_ARRAY ioctl to be sent there will be nothing to flush. However if we open /dev/mdX in order to send the STOP_ARRAY ioctl just moments before some other process which was writing closes their file descriptor, then there won't be a 'last close' and the buffers might not get flushed. So do_md_stop() calls sync_blockdev(). However at this point it is holding ->reconfig_mutex. So if the array is currently 'clean' then the writes from sync_blockdev() will not complete until the array can be marked dirty and that won't happen until some other thread can get ->reconfig_mutex. So we deadlock. We need to move the sync_blockdev() call to before we take ->reconfig_mutex. However then some other thread could open /dev/mdX and write to it after we call sync_blockdev() and before we actually stop the array. This can leave dirty data in the page cache which is awkward. So introduce new flag MD_STILL_CLOSED. Set it before calling sync_blockdev(), clear it if anyone does open the file, and abort the STOP_ARRAY attempt if it gets set before we lock against further opens. It is still possible to get problems if you open /dev/mdX, write to it, then issue the STOP_ARRAY ioctl. Just don't do that. Signed-off-by: NeilBrown <neilb@suse.de>
-rw-r--r--drivers/md/md.c39
-rw-r--r--drivers/md/md.h3
2 files changed, 33 insertions, 9 deletions
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 084a6540a4bd..adf4d7e1d5e1 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5337,8 +5337,14 @@ static int md_set_readonly(struct mddev *mddev, struct block_device *bdev)
err = -EBUSY;
goto out;
}
- if (bdev)
- sync_blockdev(bdev);
+ if (bdev && !test_bit(MD_STILL_CLOSED, &mddev->flags)) {
+ /* Someone opened the device since we flushed it
+ * so page cache could be dirty and it is too late
+ * to flush. So abort
+ */
+ mutex_unlock(&mddev->open_mutex);
+ return -EBUSY;
+ }
if (mddev->pers) {
__md_stop_writes(mddev);
@@ -5373,14 +5379,14 @@ static int do_md_stop(struct mddev * mddev, int mode,
mutex_unlock(&mddev->open_mutex);
return -EBUSY;
}
- if (bdev)
- /* It is possible IO was issued on some other
- * open file which was closed before we took ->open_mutex.
- * As that was not the last close __blkdev_put will not
- * have called sync_blockdev, so we must.
+ if (bdev && !test_bit(MD_STILL_CLOSED, &mddev->flags)) {
+ /* Someone opened the device since we flushed it
+ * so page cache could be dirty and it is too late
+ * to flush. So abort
*/
- sync_blockdev(bdev);
-
+ mutex_unlock(&mddev->open_mutex);
+ return -EBUSY;
+ }
if (mddev->pers) {
if (mddev->ro)
set_disk_ro(disk, 0);
@@ -6417,6 +6423,20 @@ static int md_ioctl(struct block_device *bdev, fmode_t mode,
!test_bit(MD_RECOVERY_NEEDED,
&mddev->flags),
msecs_to_jiffies(5000));
+ if (cmd == STOP_ARRAY || cmd == STOP_ARRAY_RO) {
+ /* Need to flush page cache, and ensure no-one else opens
+ * and writes
+ */
+ mutex_lock(&mddev->open_mutex);
+ if (atomic_read(&mddev->openers) > 1) {
+ mutex_unlock(&mddev->open_mutex);
+ err = -EBUSY;
+ goto abort;
+ }
+ set_bit(MD_STILL_CLOSED, &mddev->flags);
+ mutex_unlock(&mddev->open_mutex);
+ sync_blockdev(bdev);
+ }
err = mddev_lock(mddev);
if (err) {
printk(KERN_INFO
@@ -6670,6 +6690,7 @@ static int md_open(struct block_device *bdev, fmode_t mode)
err = 0;
atomic_inc(&mddev->openers);
+ clear_bit(MD_STILL_CLOSED, &mddev->flags);
mutex_unlock(&mddev->open_mutex);
check_disk_change(bdev);
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 53283beda21b..608050c43f17 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -211,6 +211,9 @@ struct mddev {
#define MD_CHANGE_PENDING 2 /* switch from 'clean' to 'active' in progress */
#define MD_UPDATE_SB_FLAGS (1 | 2 | 4) /* If these are set, md_update_sb needed */
#define MD_ARRAY_FIRST_USE 3 /* First use of array, needs initialization */
+#define MD_STILL_CLOSED 4 /* If set, then array has not been opened since
+ * md_ioctl checked on it.
+ */
int suspended;
atomic_t active_io;