linux-kernel - [PATCH 4.14 077/193] md: dont check MD_SB_CHANGE_CLEAN in md_allow

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Date:   Tue, 28 Nov 2017 11:25:24 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Artur Paszkiewicz <artur.paszkiewicz@...el.com>,
        Shaohua Li <shli@...com>
Subject: [PATCH 4.14 077/193] md: dont check MD_SB_CHANGE_CLEAN in md_allow_write

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

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

From: Artur Paszkiewicz <artur.paszkiewicz@...el.com>

commit b90f6ff080c52e2f05364210733df120e3c4e597 upstream.

Only MD_SB_CHANGE_PENDING should be used to wait for transition from
clean to dirty. Checking also MD_SB_CHANGE_CLEAN is unnecessary and can
race with e.g. md_do_sync(). This sporadically causes a hang when
changing consistency policy during resync:

INFO: task mdadm:6183 blocked for more than 30 seconds.
      Not tainted 4.14.0-rc3+ #391
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
mdadm           D12752  6183   6022 0x00000000
Call Trace:
 __schedule+0x93f/0x990
 schedule+0x6b/0x90
 md_allow_write+0x100/0x130 [md_mod]
 ? do_wait_intr_irq+0x90/0x90
 resize_stripes+0x3a/0x5b0 [raid456]
 ? kernfs_fop_write+0xbe/0x180
 raid5_change_consistency_policy+0xa6/0x200 [raid456]
 consistency_policy_store+0x2e/0x70 [md_mod]
 md_attr_store+0x90/0xc0 [md_mod]
 sysfs_kf_write+0x42/0x50
 kernfs_fop_write+0x119/0x180
 __vfs_write+0x28/0x110
 ? rcu_sync_lockdep_assert+0x12/0x60
 ? __sb_start_write+0x15a/0x1c0
 ? vfs_write+0xa3/0x1a0
 vfs_write+0xb4/0x1a0
 SyS_write+0x49/0xa0
 entry_SYSCALL_64_fastpath+0x18/0xad

Fixes: 2214c260c72b ("md: don't return -EAGAIN in md_allow_write for external metadata arrays")
Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@...el.com>
Signed-off-by: Shaohua Li <shli@...com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/md/md.c |    1 -
 1 file changed, 1 deletion(-)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8111,7 +8111,6 @@ void md_allow_write(struct mddev *mddev)
 		sysfs_notify_dirent_safe(mddev->sysfs_state);
 		/* wait for the dirty state to be recorded in the metadata */
 		wait_event(mddev->sb_wait,
-			   !test_bit(MD_SB_CHANGE_CLEAN, &mddev->sb_flags) &&
 			   !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags));
 	} else
 		spin_unlock(&mddev->lock);