[PATCH 1/2] f2fs: avoid race in between atomic_read & atomic_inc

[Chao Yu]

Previously, we will miss merging flush command during fsync due to below
race condition:

Thread AThread BThread C
- f2fs_issue_flush
 - atomic_read(_flush)
- f2fs_issue_flush
 - atomic_read(_flush)
- f2fs_issue_flush
 - atomic_read(_flush)
  - atomic_inc(_flush)
  - atomic_inc(_flush)
  - atomic_inc(_flush)
   - submit_flush_wait
   - submit_flush_wait
   - submit_flush_wait

It needs to use atomic_inc_return instead to avoid such race.

Signed-off-by: Chao Yu 
---
 fs/f2fs/segment.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index d6c3f456ea51..1215ca1bd4e2 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -536,8 +536,7 @@ int f2fs_issue_flush(struct f2fs_sb_info *sbi)
return ret;
}
 
-   if (!atomic_read(>issing_flush)) {
-   atomic_inc(>issing_flush);
+   if (atomic_inc_return(>issing_flush) == 1) {
ret = submit_flush_wait(sbi);
atomic_dec(>issing_flush);
 
@@ -547,7 +546,6 @@ int f2fs_issue_flush(struct f2fs_sb_info *sbi)
 
init_completion();
 
-   atomic_inc(>issing_flush);
llist_add(, >issue_list);
 
/* update issue_list before we wake up issue_flush thread */
-- 
2.13.1.388.g69e6b9b4f4a9

[PATCH 1/2] f2fs: avoid race in between atomic_read & atomic_inc

[Chao Yu]

Previously, we will miss merging flush command during fsync due to below
race condition:

Thread AThread BThread C
- f2fs_issue_flush
 - atomic_read(_flush)
- f2fs_issue_flush
 - atomic_read(_flush)
- f2fs_issue_flush
 - atomic_read(_flush)
  - atomic_inc(_flush)
  - atomic_inc(_flush)
  - atomic_inc(_flush)
   - submit_flush_wait
   - submit_flush_wait
   - submit_flush_wait

It needs to use atomic_inc_return instead to avoid such race.

Signed-off-by: Chao Yu 
---
 fs/f2fs/segment.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index d6c3f456ea51..1215ca1bd4e2 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -536,8 +536,7 @@ int f2fs_issue_flush(struct f2fs_sb_info *sbi)
return ret;
}
 
-   if (!atomic_read(>issing_flush)) {
-   atomic_inc(>issing_flush);
+   if (atomic_inc_return(>issing_flush) == 1) {
ret = submit_flush_wait(sbi);
atomic_dec(>issing_flush);
 
@@ -547,7 +546,6 @@ int f2fs_issue_flush(struct f2fs_sb_info *sbi)
 
init_completion();
 
-   atomic_inc(>issing_flush);
llist_add(, >issue_list);
 
/* update issue_list before we wake up issue_flush thread */
-- 
2.13.1.388.g69e6b9b4f4a9