Shaohua Li 於 2018-02-22 01:56 寫到:
On Wed, Feb 21, 2018 at 09:26:55AM +0800, bingjingc wrote:
There is a potential deadlock if mount/umount happens when
raid5_finish_reshape() tries to grow the size of emulated disk.
How the deadlock happens?
1) The raid5 resync thread finished reshape (expanding array).
2) The mount or umount thread holds VFS sb->s_umount lock and tries to
write through critical data into raid5 emulated block device. So it
waits for raid5 kernel thread handling stripes in order to finish
it
I/Os.
3) In the routine of raid5 kernel thread, md_check_recovery() will be
called first in order to reap the raid5 resync thread. That is,
raid5_finish_reshape() will be called. In this function, it will
try
to update conf and call VFS revalidate_disk() to grow the raid5
emulated block device. It will try to acquire VFS sb->s_umount
lock.
The raid5 kernel thread cannot continue, so no one can handle mount/
umount I/Os (stripes). Once the write-through I/Os cannot be finished,
mount/umount will not release sb->s_umount lock. The deadlock happens.
The raid5 kernel thread is an emulated block device. It is responible
to
handle I/Os (stripes) from upper layers. The emulated block device
should not request any I/Os on itself. That is, it should not call VFS
layer functions. (If it did, it will try to acquire VFS locks to
guarantee the I/Os sequence.) So we have the resync thread to send
resync I/O requests and to wait for the results.
For solving this potential deadlock, we can put the size growth of the
emulated block device as the final step of reshape thread.
2017/12/29:
Thanks to Guoqing Jiang <gqjiang@xxxxxxxx>,
we confirmed that there is the same deadlock issue in raid10. It's
reproducible and can be fixed by this patch. For raid10.c, we can
remove
the similar code to prevent deadlock as well since they has been
called
before.
Reported-by: Alex Wu <alexwu@xxxxxxxxxxxx>
Reviewed-by: Alex Wu <alexwu@xxxxxxxxxxxx>
Reviewed-by: Chung-Chiang Cheng <cccheng@xxxxxxxxxxxx>
Signed-off-by: BingJing Chang <bingjingc@xxxxxxxxxxxx>
git am still complains the patch is corrupted. probably fix your email
client?
Sorry, I'm new here, and I sent patch via web email client in plain text
mode. I resent it via git send-email and confirmed it could be applied.
Please apply the latest one, thank you.
Thanks,
BingJing
---
drivers/md/md.c | 13 +++++++++++++
drivers/md/raid10.c | 8 +-------
drivers/md/raid5.c | 8 +-------
3 files changed, 15 insertions(+), 14 deletions(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 4e4dee0..52092de 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8528,6 +8528,19 @@ void md_do_sync(struct md_thread *thread)
set_mask_bits(&mddev->sb_flags, 0,
BIT(MD_SB_CHANGE_PENDING) | BIT(MD_SB_CHANGE_DEVS));
+ if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
+ !test_bit(MD_RECOVERY_INTR, &mddev->recovery) &&
+ mddev->delta_disks > 0 &&
+ mddev->pers->finish_reshape &&
+ mddev->pers->size &&
+ mddev->queue) {
+ mddev_lock_nointr(mddev);
+ md_set_array_sectors(mddev, mddev->pers->size(mddev, 0, 0));
+ mddev_unlock(mddev);
+ set_capacity(mddev->gendisk, mddev->array_sectors);
+ revalidate_disk(mddev->gendisk);
+ }
+
spin_lock(&mddev->lock);
if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery)) {
/* We completed so min/max setting can be forgotten if used. */
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index c131835..8a46473 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -4818,17 +4818,11 @@ static void raid10_finish_reshape(struct mddev
*mddev)
return;
if (mddev->delta_disks > 0) {
- sector_t size = raid10_size(mddev, 0, 0);
- md_set_array_sectors(mddev, size);
if (mddev->recovery_cp > mddev->resync_max_sectors) {
mddev->recovery_cp = mddev->resync_max_sectors;
set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
}
- mddev->resync_max_sectors = size;
- if (mddev->queue) {
- set_capacity(mddev->gendisk, mddev->array_sectors);
- revalidate_disk(mddev->gendisk);
- }
+ mddev->resync_max_sectors = mddev->array_sectors;
} else {
int d;
rcu_read_lock();
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 98ce427..0f68faa 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -8001,13 +8001,7 @@ static void raid5_finish_reshape(struct mddev
*mddev)
if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery)) {
- if (mddev->delta_disks > 0) {
- md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));
- if (mddev->queue) {
- set_capacity(mddev->gendisk, mddev->array_sectors);
- revalidate_disk(mddev->gendisk);
- }
- } else {
+ if (mddev->delta_disks <= 0) {
int d;
spin_lock_irq(&conf->device_lock);
mddev->degraded = raid5_calc_degraded(conf);
--
2.7.4
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