linux-kernel - Re: [f2fs-dev] [PATCH 1/2 v2] f2fs: avoid deadlock caused by lock order of page and lock

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Date:   Fri, 7 Jul 2017 12:13:59 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 1/2 v2] f2fs: avoid deadlock caused by lock
 order of page and lock_op

- punch_hole
 - fill_zero
  - f2fs_lock_op
  - get_new_data_page
   - lock_page

- f2fs_write_data_pages
 - lock_page
 - do_write_data_page
  - f2fs_lock_op

Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
---

 Change log from v1:
 - hide EAGAIN to users

 fs/f2fs/data.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 72fc866cad19..7dd5fb647d43 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1404,8 +1404,9 @@ int do_write_data_page(struct f2fs_io_info *fio)
 		}
 	}
 
-	if (fio->need_lock == LOCK_REQ)
-		f2fs_lock_op(fio->sbi);
+	/* Deadlock due to between page->lock and f2fs_lock_op */
+	if (fio->need_lock == LOCK_REQ && !f2fs_trylock_op(fio->sbi))
+		return -EAGAIN;
 
 	err = get_dnode_of_data(&dn, page->index, LOOKUP_NODE);
 	if (err)
@@ -1667,7 +1668,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 			}
 
 			done_index = page->index;
-
+retry_write:
 			lock_page(page);
 
 			if (unlikely(page->mapping != mapping)) {
@@ -1703,6 +1704,15 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 					unlock_page(page);
 					ret = 0;
 					continue;
+				} else if (ret == -EAGAIN) {
+					ret = 0;
+					if (wbc->sync_mode == WB_SYNC_ALL) {
+						cond_resched();
+						congestion_wait(BLK_RW_ASYNC,
+									HZ/50);
+						goto retry_write;
+					}
+					continue;
 				}
 				done_index = page->index + 1;
 				done = 1;
-- 
2.13.0.rc1.294.g07d810a77f-goog