linux-kernel - [PATCH 4.9 024/116] staging/lustre/osc: Revert erroneous list_for_each_entry

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Message-Id: <20170106213910.003568611@linuxfoundation.org>
Date:   Fri,  6 Jan 2017 22:43:06 +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,
        Bhaktipriya Shridhar <bhaktipriya96@...il.com>,
        Oleg Drokin <green@...uxhacker.ru>
Subject: [PATCH 4.9 024/116] staging/lustre/osc: Revert erroneous list_for_each_entry_safe use

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

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

From: Oleg Drokin <green@...uxhacker.ru>

commit cd15dd6ef4ea11df87f717b8b1b83aaa738ec8af upstream.

I have been having a lot of unexplainable crashes in osc_lru_shrink
lately that I could not see a good explanation for and then I found
this patch that slip under the radar somehow that incorrectly
converted while loop for lru list iteration into
list_for_each_entry_safe totally ignoring that in the body of
the loop we drop spinlocks guarding this list and move list entries
around.
Not sure why it was not showing up right away, perhaps some of the
more recent LRU changes committed caused some extra pressure on this
code that finally highlighted the breakage.

Reverts: 8adddc36b1fc ("staging: lustre: osc: Use list_for_each_entry_safe")
CC: Bhaktipriya Shridhar <bhaktipriya96@...il.com>
Signed-off-by: Oleg Drokin <green@...uxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/staging/lustre/lustre/osc/osc_page.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/staging/lustre/lustre/osc/osc_page.c
+++ b/drivers/staging/lustre/lustre/osc/osc_page.c
@@ -542,7 +542,6 @@ long osc_lru_shrink(const struct lu_env
 	struct cl_object *clobj = NULL;
 	struct cl_page **pvec;
 	struct osc_page *opg;
-	struct osc_page *temp;
 	int maxscan = 0;
 	long count = 0;
 	int index = 0;
@@ -569,13 +568,15 @@ long osc_lru_shrink(const struct lu_env
 
 	spin_lock(&cli->cl_lru_list_lock);
 	maxscan = min(target << 1, atomic_long_read(&cli->cl_lru_in_list));
-	list_for_each_entry_safe(opg, temp, &cli->cl_lru_list, ops_lru) {
+	while (!list_empty(&cli->cl_lru_list)) {
 		struct cl_page *page;
 		bool will_free = false;
 
 		if (--maxscan < 0)
 			break;
 
+		opg = list_entry(cli->cl_lru_list.next, struct osc_page,
+				 ops_lru);
 		page = opg->ops_cl.cpl_page;
 		if (lru_page_busy(cli, page)) {
 			list_move_tail(&opg->ops_lru, &cli->cl_lru_list);