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md: Close race when setting 'action' to 'idle'. 

Checking ->sync_thread without holding the mddev_lock()
isn't really safe, even after flushing the workqueue which
ensures md_start_sync() has been run.

While this code is waiting for the lock, md_check_recovery could reap
the thread itself, and then start another thread (e.g. recovery might
finish, then reshape starts).  When this thread gets the lock
md_start_sync() hasn't run so it doesn't get reaped, but
MD_RECOVERY_RUNNING gets cleared.  This allows two threads to start
which leads to confusion.

So don't both if MD_RECOVERY_RUNNING isn't set, but if it is do
the flush and the test and the reap all under the mddev_lock to
avoid any race with md_check_recovery.

Signed-off-by: NeilBrown <neilb@suse.de>
Fixes: 6791875e2e ("md: make reconfig_mutex optional for writes to md sysfs files.")
Cc: stable@vger.kernel.org (v4.0+)
This commit is contained in:
NeilBrown 2015-06-12 19:51:27 +10:00
parent c008f1d356
commit 8e8e2518fc
1 changed files with 6 additions and 5 deletions
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5
drivers/md/md.c
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@ -4217,13 +4217,14 @@ action_store(struct mddev *mddev, const char *page, size_t len)
set_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
else
clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery);
if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) &&
mddev_lock(mddev) == 0) {
flush_workqueue(md_misc_wq);
if (mddev->sync_thread) {
set_bit(MD_RECOVERY_INTR, &mddev->recovery);
if (mddev_lock(mddev) == 0) {
md_reap_sync_thread(mddev);
mddev_unlock(mddev);
}
mddev_unlock(mddev);
}
} else if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) ||
test_bit(MD_RECOVERY_NEEDED, &mddev->recovery))