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Subject[PATCH 4.14 088/496] md: fix md_write_start() deadlock w/o metadata devices
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Heinz Mauelshagen <heinzm@redhat.com>

[ Upstream commit 4b6c1060eaa6495aa5b0032e8f2d51dd936b1257 ]

If no metadata devices are configured on raid1/4/5/6/10
(e.g. via dm-raid), md_write_start() unconditionally waits
for superblocks to be written thus deadlocking.

Fix introduces mddev->has_superblocks bool, defines it in md_run()
and checks for it in md_write_start() to conditionally avoid waiting.

Once on it, check for non-existing superblocks in md_super_write().

Link: https://bugzilla.kernel.org/show_bug.cgi?id=198647
Fixes: cc27b0c78c796 ("md: fix deadlock between mddev_suspend() and md_write_start()")

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Shaohua Li <sh.li@alibaba-inc.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/md/md.c | 10 ++++++++++
drivers/md/md.h | 2 ++
2 files changed, 12 insertions(+)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -779,6 +779,9 @@ void md_super_write(struct mddev *mddev,
struct bio *bio;
int ff = 0;

+ if (!page)
+ return;
+
if (test_bit(Faulty, &rdev->flags))
return;

@@ -5434,6 +5437,7 @@ int md_run(struct mddev *mddev)
* the only valid external interface is through the md
* device.
*/
+ mddev->has_superblocks = false;
rdev_for_each(rdev, mddev) {
if (test_bit(Faulty, &rdev->flags))
continue;
@@ -5447,6 +5451,9 @@ int md_run(struct mddev *mddev)
set_disk_ro(mddev->gendisk, 1);
}

+ if (rdev->sb_page)
+ mddev->has_superblocks = true;
+
/* perform some consistency tests on the device.
* We don't want the data to overlap the metadata,
* Internal Bitmap issues have been handled elsewhere.
@@ -8022,6 +8029,7 @@ EXPORT_SYMBOL(md_done_sync);
bool md_write_start(struct mddev *mddev, struct bio *bi)
{
int did_change = 0;
+
if (bio_data_dir(bi) != WRITE)
return true;

@@ -8054,6 +8062,8 @@ bool md_write_start(struct mddev *mddev,
rcu_read_unlock();
if (did_change)
sysfs_notify_dirent_safe(mddev->sysfs_state);
+ if (!mddev->has_superblocks)
+ return true;
wait_event(mddev->sb_wait,
!test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags) ||
mddev->suspended);
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -462,6 +462,8 @@ struct mddev {
void (*sync_super)(struct mddev *mddev, struct md_rdev *rdev);
struct md_cluster_info *cluster_info;
unsigned int good_device_nr; /* good device num within cluster raid */
+
+ bool has_superblocks:1;
};

enum recovery_flags {

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