Hi chao:
As I mentioned before,
https://lore.kernel.org/linux-f2fs-devel/kl1pr0601mb400309c5d62bfddde6aad8aebb...@kl1pr0601mb4003.apcprd06.prod.outlook.com/T/#mbe9a8f27626ac7ca71035e25f5502e756ab877ac
there is a potential dead lock problem when just remove
compress file condition in __should_serialize_io().
The modify like this:
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 9f754aaef558..ffbee94924f3 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -3218,8 +3224,6 @@ static inline bool __should_serialize_io(struct inode
*inode,
if (IS_NOQUOTA(inode))
return false;
- if (f2fs_need_compress_data(inode))
- return true;
if (wbc->sync_mode != WB_SYNC_ALL)
return true;
This modification is a prerequisite, if there is no modification there is no
problem for now.
And I make a debug, and here is what I found:
Thread 1 is doing checkpoint in below procedure:
Thread 2 Thread 3
f2fs_write_cache_pages page 0
->lock_page(page) page 0-3 f2fs_write_cache_pages
page 0
->f2fs_write_compressed_pages
->lock_page(page) //lock page 0, sleep
->f2fs_trylock_op failed
->f2fs_write_raw_pages
->f2fs_write_single_data_page
->f2fs_trylock_op failed
->unlock(page) page 0
->cond_resched();
->lock_page(page) //lock page 0 success
->lock_page(page) //try page 1,
->lock_page(page); page 0 //never success
When Thread 1 do checkpoint and down_write of cp_rwsem, Thread 2 and Thread 3
are write same cluster, Thread 2 start write cache page first, and get lock
page 0-3, beacuse of f2fs_trylock_op failed, f2fs_write_compressed_pages and
f2fs_write_single_data_page will failed, and Thread 2 will unlock page 0, but
keep lock page 1-3 and schedule out, if thread 3 start write cache page in
this time, thread 3 could get lock of page 0, but when try lock of page 1, it
would never success. Then a deadlock occured between thread 2 and Thread 3.
So, there is a potential limit: We can't write same clutser is multithread for
compressed file .
If we need to fix this problem, my thoughts is we shoudn't unlcok page in
f2fs_write_single_data_page for compress raw page.
Do we need to fix this for now?)
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