Re: crash: write_sb_page walks mddev.disks without holding reconfig_mutex | |
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On Monday July 14, Nate.Dailey@xxxxxxxxxxx wrote:
> Hitting several related crashes, and looking for advice/help...
>
> I'm using MD raid1 under RHEL 5 update 2 (kernel 2.6.18-92.el5). I've
> also incorporated a few upstream patches to address various bugs, but
> don't believe any of these are causing what I'm now seeing.
>
> I've hit 3 different crashes that all involve an rdev being ripped out
> from under someone walking the mddev.disks list. It looks like the
> reconfig_mutex is supposed to prevent this.
Thanks for reporting this.
You are right. The mddev.disks list is not being protected properly.
It is only ever changed under reconfig_mutex, and lots of the accesses
are under the same mutex. However I count three that are not:
write_sb_page (which you found)
match_mddev_units
is_mddev_idle
It is not really appropriate to take reconfig_mutex in these cases.
I think the best fix would be to use the 'rcu' approach.
The following patch attempts that. If you could test it I would
really appreciate it.
Thanks,
NeilBrown
commit ec54a752a284ee3ace5177935bc0385c5ee2c70c
Author: Neil Brown <neilb@xxxxxxx>
Date: Tue Jul 15 10:35:28 2008 +1000
Protect access to mddev->disks list using RCU
All modifications and most access to the mddev->disks list are made
under the reconfig_mutex lock. However there are three places where
the list is walked without any locking. If a reconfig happens at this
time, havoc (and oops) can ensue.
So use RCU to protect these accesses:
- wrap them in rcu_read_{,un}lock()
- use list_for_each_entry_rcu
- add to the list with list_add_rcu
- delete from the list with list_del_rcu
- delay the 'free' with call_rcu rather than schedule_work
Note that export_rdev did a list_del_init on this list. In almost all
cases the entry was not in the list anymore so it was a no-op and so
safe. It is no longer safe as after list_del_rcu we may not touch
the list_head.
An audit shows that export_rdev is called:
- after unbind_rdev_from_array, in which case the delete has
already been done,
- after bind_rdev_to_array fails, in which case the delete isn't needed.
- before the device has been put on a list at all (e.g. in
add_new_disk where reading the superblock fails).
- and in autorun devices after a failure when the device is on a
different list.
So remove the list_del_init call from export_rdev, and add it back
immediately before the called to export_rdev for that last case.
Note also that ->same_set is sometimes used for lists other than
mddev->list (e.g. candidates). In these cases rcu is not needed.
Signed-off-by: NeilBrown <neilb@xxxxxxx>
diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index eba83e2..621a272 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -241,10 +241,10 @@ static struct page *read_sb_page(mddev_t *mddev, long offset, unsigned long inde
static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
{
mdk_rdev_t *rdev;
- struct list_head *tmp;
mddev_t *mddev = bitmap->mddev;
- rdev_for_each(rdev, tmp, mddev)
+ rcu_read_lock();
+ rdev_for_each_rcu(rdev, mddev)
if (test_bit(In_sync, &rdev->flags)
&& !test_bit(Faulty, &rdev->flags)) {
int size = PAGE_SIZE;
@@ -260,11 +260,11 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
+ (long)(page->index * (PAGE_SIZE/512))
+ size/512 > 0)
/* bitmap runs in to metadata */
- return -EINVAL;
+ goto bad_alignment;
if (rdev->data_offset + mddev->size*2
> rdev->sb_start + bitmap->offset)
/* data runs in to bitmap */
- return -EINVAL;
+ goto bad_alignment;
} else if (rdev->sb_start < rdev->data_offset) {
/* METADATA BITMAP DATA */
if (rdev->sb_start
@@ -272,7 +272,7 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
+ page->index*(PAGE_SIZE/512) + size/512
> rdev->data_offset)
/* bitmap runs in to data */
- return -EINVAL;
+ goto bad_alignment;
} else {
/* DATA METADATA BITMAP - no problems */
}
@@ -282,10 +282,15 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
size,
page);
}
+ rcu_read_unlock();
if (wait)
md_super_wait(mddev);
return 0;
+
+ bad_alignment:
+ rcu_read_unlock();
+ return -EINVAL;
}
static void bitmap_file_kick(struct bitmap *bitmap);
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 7dcdff6..66ca159 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1397,15 +1397,17 @@ static struct super_type super_types[] = {
static int match_mddev_units(mddev_t *mddev1, mddev_t *mddev2)
{
- struct list_head *tmp, *tmp2;
mdk_rdev_t *rdev, *rdev2;
- rdev_for_each(rdev, tmp, mddev1)
- rdev_for_each(rdev2, tmp2, mddev2)
+ rcu_read_lock();
+ rdev_for_each_rcu(rdev, mddev1)
+ rdev_for_each_rcu(rdev2, mddev2)
if (rdev->bdev->bd_contains ==
- rdev2->bdev->bd_contains)
+ rdev2->bdev->bd_contains) {
+ rcu_read_unlock();
return 1;
-
+ }
+ rcu_read_unlock();
return 0;
}
@@ -1472,7 +1474,7 @@ static int bind_rdev_to_array(mdk_rdev_t * rdev, mddev_t * mddev)
kobject_del(&rdev->kobj);
goto fail;
}
- list_add(&rdev->same_set, &mddev->disks);
+ list_add_rcu(&rdev->same_set, &mddev->disks);
bd_claim_by_disk(rdev->bdev, rdev->bdev->bd_holder, mddev->gendisk);
return 0;
@@ -1482,9 +1484,9 @@ static int bind_rdev_to_array(mdk_rdev_t * rdev, mddev_t * mddev)
return err;
}
-static void md_delayed_delete(struct work_struct *ws)
+static void md_delayed_delete(struct rcu_head *rcu)
{
- mdk_rdev_t *rdev = container_of(ws, mdk_rdev_t, del_work);
+ mdk_rdev_t *rdev = container_of(rcu, mdk_rdev_t, rcu_work);
kobject_del(&rdev->kobj);
kobject_put(&rdev->kobj);
}
@@ -1497,17 +1499,17 @@ static void unbind_rdev_from_array(mdk_rdev_t * rdev)
return;
}
bd_release_from_disk(rdev->bdev, rdev->mddev->gendisk);
- list_del_init(&rdev->same_set);
+ list_del_rcu(&rdev->same_set);
printk(KERN_INFO "md: unbind<%s>\n", bdevname(rdev->bdev,b));
rdev->mddev = NULL;
sysfs_remove_link(&rdev->kobj, "block");
/* We need to delay this, otherwise we can deadlock when
- * writing to 'remove' to "dev/state"
+ * writing to 'remove' to "dev/state". We also need
+ * to delay it due to rcu usage.
*/
- INIT_WORK(&rdev->del_work, md_delayed_delete);
kobject_get(&rdev->kobj);
- schedule_work(&rdev->del_work);
+ call_rcu(&rdev->rcu_work, md_delayed_delete);
}
/*
@@ -1560,7 +1562,6 @@ static void export_rdev(mdk_rdev_t * rdev)
if (rdev->mddev)
MD_BUG();
free_disk_sb(rdev);
- list_del_init(&rdev->same_set);
#ifndef MODULE
if (test_bit(AutoDetected, &rdev->flags))
md_autodetect_dev(rdev->bdev->bd_dev);
@@ -4063,8 +4064,10 @@ static void autorun_devices(int part)
/* on success, candidates will be empty, on error
* it won't...
*/
- rdev_for_each_list(rdev, tmp, candidates)
+ rdev_for_each_list(rdev, tmp, candidates) {
+ list_del_init(&rdev->same_set);
export_rdev(rdev);
+ }
mddev_put(mddev);
}
printk(KERN_INFO "md: ... autorun DONE.\n");
@@ -5528,12 +5531,12 @@ int unregister_md_personality(struct mdk_personality *p)
static int is_mddev_idle(mddev_t *mddev)
{
mdk_rdev_t * rdev;
- struct list_head *tmp;
int idle;
long curr_events;
idle = 1;
- rdev_for_each(rdev, tmp, mddev) {
+ rcu_read_lock();
+ rdev_for_each_rcu(rdev, mddev) {
struct gendisk *disk = rdev->bdev->bd_contains->bd_disk;
curr_events = disk_stat_read(disk, sectors[0]) +
disk_stat_read(disk, sectors[1]) -
@@ -5565,6 +5568,7 @@ static int is_mddev_idle(mddev_t *mddev)
idle = 0;
}
}
+ rcu_read_unlock();
return idle;
}
diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index 35da93c..6fa94ff 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -114,7 +114,7 @@ struct mdk_rdev_s
* for reporting to userspace and storing
* in superblock.
*/
- struct work_struct del_work; /* used for delayed sysfs removal */
+ struct rcu_head rcu_work; /* used for delayed sysfs removal */
};
struct mddev_s
@@ -339,6 +339,9 @@ static inline char * mdname (mddev_t * mddev)
#define rdev_for_each(rdev, tmp, mddev) \
rdev_for_each_list(rdev, tmp, (mddev)->disks)
+#define rdev_for_each_rcu(rdev, mddev) \
+ list_for_each_entry_rcu(rdev, &((mddev)->disks), same_set)
+
typedef struct mdk_thread_s {
void (*run) (mddev_t *mddev);
mddev_t *mddev;
--
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