[patch 41/59] md: fix potential memalloc deadlock in md

Chris Wright
2007-02-03T02:39:46Z

[-- Attachment #1: md-fix-potential-memalloc-deadlock-in-md.patch --]
[-- Type: text/plain, Size: 3351 bytes --]

-stable review patch. If anyone has any objections, please let us know.
------------------

From: NeilBrown <neilb@suse.de>

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@suse.de>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
---
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(-)

--- linux-2.6.19.2.orig/drivers/md/md.c
+++ linux-2.6.19.2/drivers/md/md.c
@@ -3561,6 +3561,8 @@ 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;
@@ -5029,6 +5031,33 @@ 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
--- linux-2.6.19.2.orig/drivers/md/raid1.c
+++ linux-2.6.19.2/drivers/md/raid1.c
@@ -2104,6 +2104,8 @@ 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) {
--- linux-2.6.19.2.orig/drivers/md/raid5.c
+++ linux-2.6.19.2/drivers/md/raid5.c
@@ -403,6 +403,8 @@ 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),
@@ -3045,6 +3047,7 @@ 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++;
--- linux-2.6.19.2.orig/include/linux/raid/md.h
+++ linux-2.6.19.2/include/linux/raid/md.h
@@ -94,7 +94,7 @@ 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

--