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Subject[PATCH v2 5/7] VFS: Avoid read-write deadlock in try_to_writeback_inodes_sb
Date
From: Valerie Aurora <val@vaaconsulting.com>

Use trylock in try_to_writeback_inodes_sb to avoid read-write
deadlocks that could be triggered by freeze.

BugLink: https://bugs.launchpad.net/bugs/897421
Signed-off-by: Valerie Aurora <val@vaaconsulting.com>
Cc: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
[kamal@canonical.com: patch restructure]
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
fs/fs-writeback.c | 13 ++++++++-----
1 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index ea89b3f..3a80f1b 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1274,8 +1274,9 @@ EXPORT_SYMBOL(writeback_inodes_sb);
* try_to_writeback_inodes_sb - start writeback if none underway
* @sb: the superblock
*
- * Invoke writeback_inodes_sb if no writeback is currently underway.
- * Returns 1 if writeback was started, 0 if not.
+ * Invoke writeback_inodes_sb if no writeback is currently underway
+ * and no one else holds the s_umount lock. Returns 1 if writeback
+ * was started, 0 if not.
*/
int try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
{
@@ -1288,15 +1289,17 @@ EXPORT_SYMBOL(try_to_writeback_inodes_sb);
* @sb: the superblock
* @nr: the number of pages to write
*
- * Invoke writeback_inodes_sb if no writeback is currently underway.
- * Returns 1 if writeback was started, 0 if not.
+ * Invoke writeback_inodes_sb if no writeback is currently underway
+ * and no one else holds the s_umount lock. Returns 1 if writeback
+ * was started, 0 if not.
*/
int try_to_writeback_inodes_sb_nr(struct super_block *sb,
unsigned long nr,
enum wb_reason reason)
{
if (!writeback_in_progress(sb->s_bdi)) {
- down_read(&sb->s_umount);
+ if (!down_read_trylock(&sb->s_umount))
+ return 0;
if (nr == 0)
writeback_inodes_sb(sb, reason);
else
--
1.7.5.4


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