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Date: Thu, 25 Jan 2007 15:19:37 +1100
From: NeilBrown <neilb@...e.de>
To: Andrew Morton <akpm@...l.org>
Cc: linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] md: Fix potential memalloc deadlock in md
Another md patch suitable for 2.6.20.
Thanks,
NeilBrown
### Comments for Changeset
If a GFP_KERNEL allocation is attempted in md while the mddev_lock is
held, it is possible for a deadlock to eventuate.
This happens if the array was marked 'clean', and the memalloc triggers
a write-out to the md device.
For the writeout to succeed, the array must be marked 'dirty', and that
requires getting the mddev_lock.
So, before attempting a GFP_KERNEL alloction while holding the lock,
make sure the array is marked 'dirty' (unless it is currently read-only).
Signed-off-by: Neil Brown <neilb@...e.de>
### Diffstat output
./drivers/md/md.c | 29 +++++++++++++++++++++++++++++
./drivers/md/raid1.c | 2 ++
./drivers/md/raid5.c | 3 +++
./include/linux/raid/md.h | 2 +-
4 files changed, 35 insertions(+), 1 deletion(-)
diff .prev/drivers/md/md.c ./drivers/md/md.c
--- .prev/drivers/md/md.c 2007-01-23 11:23:58.000000000 +1100
+++ ./drivers/md/md.c 2007-01-25 12:47:58.000000000 +1100
@@ -3564,6 +3564,8 @@ static int get_bitmap_file(mddev_t * mdd
char *ptr, *buf = NULL;
int err = -ENOMEM;
+ md_allow_write(mddev);
+
file = kmalloc(sizeof(*file), GFP_KERNEL);
if (!file)
goto out;
@@ -5032,6 +5034,33 @@ void md_write_end(mddev_t *mddev)
}
}
+/* md_allow_write(mddev)
+ * Calling this ensures that the array is marked 'active' so that writes
+ * may proceed without blocking. It is important to call this before
+ * attempting a GFP_KERNEL allocation while holding the mddev lock.
+ * Must be called with mddev_lock held.
+ */
+void md_allow_write(mddev_t *mddev)
+{
+ if (!mddev->pers)
+ return;
+ if (mddev->ro)
+ return;
+
+ spin_lock_irq(&mddev->write_lock);
+ if (mddev->in_sync) {
+ mddev->in_sync = 0;
+ set_bit(MD_CHANGE_CLEAN, &mddev->flags);
+ if (mddev->safemode_delay &&
+ mddev->safemode == 0)
+ mddev->safemode = 1;
+ spin_unlock_irq(&mddev->write_lock);
+ md_update_sb(mddev, 0);
+ } else
+ spin_unlock_irq(&mddev->write_lock);
+}
+EXPORT_SYMBOL_GPL(md_allow_write);
+
static DECLARE_WAIT_QUEUE_HEAD(resync_wait);
#define SYNC_MARKS 10
diff .prev/drivers/md/raid1.c ./drivers/md/raid1.c
--- .prev/drivers/md/raid1.c 2007-01-23 11:23:43.000000000 +1100
+++ ./drivers/md/raid1.c 2007-01-25 12:09:43.000000000 +1100
@@ -2050,6 +2050,8 @@ static int raid1_reshape(mddev_t *mddev)
return -EINVAL;
}
+ md_allow_write(mddev);
+
raid_disks = mddev->raid_disks + mddev->delta_disks;
if (raid_disks < conf->raid_disks) {
diff .prev/drivers/md/raid5.c ./drivers/md/raid5.c
--- .prev/drivers/md/raid5.c 2007-01-23 11:13:44.000000000 +1100
+++ ./drivers/md/raid5.c 2007-01-25 12:18:04.000000000 +1100
@@ -399,6 +399,8 @@ static int resize_stripes(raid5_conf_t *
if (newsize <= conf->pool_size)
return 0; /* never bother to shrink */
+ md_allow_write(conf->mddev);
+
/* Step 1 */
sc = kmem_cache_create(conf->cache_name[1-conf->active_name],
sizeof(struct stripe_head)+(newsize-1)*sizeof(struct r5dev),
@@ -3195,6 +3197,7 @@ raid5_store_stripe_cache_size(mddev_t *m
else
break;
}
+ md_allow_write(mddev);
while (new > conf->max_nr_stripes) {
if (grow_one_stripe(conf))
conf->max_nr_stripes++;
diff .prev/include/linux/raid/md.h ./include/linux/raid/md.h
--- .prev/include/linux/raid/md.h 2007-01-25 12:16:57.000000000 +1100
+++ ./include/linux/raid/md.h 2007-01-25 12:17:18.000000000 +1100
@@ -93,7 +93,7 @@ extern int sync_page_io(struct block_dev
struct page *page, int rw);
extern void md_do_sync(mddev_t *mddev);
extern void md_new_event(mddev_t *mddev);
-
+extern void md_allow_write(mddev_t *mddev);
#endif /* CONFIG_MD */
#endif
-
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