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[PATCH] xfs: lock for removing item from cil->xc_cil in xlog_cil_push

To: xfs@xxxxxxxxxxx
Subject: [PATCH] xfs: lock for removing item from cil->xc_cil in xlog_cil_push
From: Xu Wang <xuw@xxxxxxxxxx>
Date: Fri, 10 Oct 2014 03:31:46 -0400 (EDT)
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <929991500.42327290.1412926226461.JavaMail.zimbra@xxxxxxxxxx>
Thread-index: AWgr59coV+eVCUv9nPbKc3KnzV7a3g==
Thread-topic: lock for removing item from cil->xc_cil in xlog_cil_push
>From 59c6babab7c4ce8708036018143d2acc1477cc7f Mon Sep 17 00:00:00 2001
From: George Wang <xuw@xxxxxxxxxx>
Date: Fri, 10 Oct 2014 15:02:14 +0800
Subject: [PATCH] [PATCH] xfs: lock for removing item from cil->xc_cil in
 xlog_cil_push

There is a race condition when xlog_cil_force_lsn and xlog_cil_push for
cil->xc_cil items. When function xlog_cil_push_now called in
xlog_cil_force_lsn, and the xlog_cil_push run in workqueue just reaches the 
point for
setting cil->xc_current_sequence, the xlog_cil_force_lsn got the lock
and check the "sequence == cil->xc_current_sequence &&
!list_empty(&cil->xc_cil)" for restart. The statement "sequence ==
cil->xc_current_sequence" is true, but the cil->xc_cil is empty
according to the xlog_cil_push removed the items in cil->xc_cil without
lock protectionl. So the function xlog_cil_force_lsn will return
NULLCOMMITLSN, which means the cil log for current sequence will not be
submitted to disk. And if there is no more operations(for example, when
unmount fs, this situation happened in
xfs_unmountfs->xfs_log_sbcount->xfs_trans_commit), the xfs will hang up.

Signed-off-by: George Wang <xuw@xxxxxxxxxx>
---
 fs/xfs/xfs_log_cil.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
index f6b79e5..97ba527 100644
--- a/fs/xfs/xfs_log_cil.c
+++ b/fs/xfs/xfs_log_cil.c
@@ -478,6 +478,8 @@ xlog_cil_push(
     */
    lv = NULL;
    num_iovecs = 0;
+
+   spin_lock(&cil->xc_push_lock);
    while (!list_empty(&cil->xc_cil)) {
        struct xfs_log_item *item;

@@ -530,7 +532,6 @@ xlog_cil_push(
     * against the current sequence in log forces without risking
     * deferencing a freed context pointer.
     */
-   spin_lock(&cil->xc_push_lock);
    cil->xc_current_sequence = new_ctx->sequence;
    list_add(&ctx->committing, &cil->xc_committing);
    spin_unlock(&cil->xc_push_lock);
-- 
1.9.3


-- 
George Wang çæ

Kernel Quantity Engineer
Red Hat Software (Beijing) Co.,Ltd
IRC:xuw
Tel:+86-010-62608041
Phone:15901231579
9/F, Tower C, Raycom

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