* [PATCH] f2fs: compress: fix potential deadlock of compress file
[not found] <CGME20211210043017epcas1p38cc53389a50e33752e97618498b18f33@epcas1p3.samsung.com>
@ 2021-12-10 4:30 ` Hyeong-Jun Kim
2021-12-10 6:32 ` [f2fs-dev] " fengnan chang
2021-12-10 14:59 ` Chao Yu
0 siblings, 2 replies; 3+ messages in thread
From: Hyeong-Jun Kim @ 2021-12-10 4:30 UTC (permalink / raw)
To: Jaegeuk Kim, Chao Yu
Cc: Hyeong-Jun Kim, Sungjong Seo, Youngjin Gil, linux-f2fs-devel,
linux-kernel
There is a potential deadlock between writeback process and a process
performing write_begin() or write_cache_pages() while trying to write
same compress file, but not compressable, as below:
[Process A] - doing checkpoint
[Process B] [Process C]
f2fs_write_cache_pages()
- lock_page() [all pages in cluster, 0-31]
- f2fs_write_multi_pages()
- f2fs_write_raw_pages()
- f2fs_write_single_data_page()
- f2fs_do_write_data_page()
- return -EAGAIN [f2fs_trylock_op() failed]
- unlock_page(page) [e.g., page 0]
- generic_perform_write()
- f2fs_write_begin()
- f2fs_prepare_compress_overwrite()
- prepare_compress_overwrite()
- lock_page() [e.g., page 0]
- lock_page() [e.g., page 1]
- lock_page(page) [e.g., page 0]
Since there is no compress process, it is no longer necessary to hold
locks on every pages in cluster within f2fs_write_raw_pages().
This patch changes f2fs_write_raw_pages() to release all locks first
and then perform write same as the non-compress file in
f2fs_write_cache_pages().
Fixes: 4c8ff7095bef ("f2fs: support data compression")
Signed-off-by: Hyeong-Jun Kim <hj514.kim@samsung.com>
Signed-off-by: Sungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: Youngjin Gil <youngjin.gil@samsung.com>
---
fs/f2fs/compress.c | 50 ++++++++++++++++++++--------------------------
1 file changed, 22 insertions(+), 28 deletions(-)
diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 7588e4e817b8..5aae63b5eb5c 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -1467,25 +1467,38 @@ static int f2fs_write_raw_pages(struct compress_ctx *cc,
enum iostat_type io_type)
{
struct address_space *mapping = cc->inode->i_mapping;
- int _submitted, compr_blocks, ret;
- int i = -1, err = 0;
+ int _submitted, compr_blocks, ret, i;
compr_blocks = f2fs_compressed_blocks(cc);
- if (compr_blocks < 0) {
- err = compr_blocks;
- goto out_err;
+
+ for (i = 0; i < cc->cluster_size; i++) {
+ if (!cc->rpages[i])
+ continue;
+
+ redirty_page_for_writepage(wbc, cc->rpages[i]);
+ unlock_page(cc->rpages[i]);
}
+ if (compr_blocks < 0)
+ return compr_blocks;
+
for (i = 0; i < cc->cluster_size; i++) {
if (!cc->rpages[i])
continue;
retry_write:
+ lock_page(cc->rpages[i]);
+
if (cc->rpages[i]->mapping != mapping) {
+continue_unlock:
unlock_page(cc->rpages[i]);
continue;
}
- BUG_ON(!PageLocked(cc->rpages[i]));
+ if (!PageDirty(cc->rpages[i]))
+ goto continue_unlock;
+
+ if (!clear_page_dirty_for_io(cc->rpages[i]))
+ goto continue_unlock;
ret = f2fs_write_single_data_page(cc->rpages[i], &_submitted,
NULL, NULL, wbc, io_type,
@@ -1500,26 +1513,15 @@ static int f2fs_write_raw_pages(struct compress_ctx *cc,
* avoid deadlock caused by cluster update race
* from foreground operation.
*/
- if (IS_NOQUOTA(cc->inode)) {
- err = 0;
- goto out_err;
- }
+ if (IS_NOQUOTA(cc->inode))
+ return 0;
ret = 0;
cond_resched();
congestion_wait(BLK_RW_ASYNC,
DEFAULT_IO_TIMEOUT);
- lock_page(cc->rpages[i]);
-
- if (!PageDirty(cc->rpages[i])) {
- unlock_page(cc->rpages[i]);
- continue;
- }
-
- clear_page_dirty_for_io(cc->rpages[i]);
goto retry_write;
}
- err = ret;
- goto out_err;
+ return ret;
}
*submitted += _submitted;
@@ -1528,14 +1530,6 @@ static int f2fs_write_raw_pages(struct compress_ctx *cc,
f2fs_balance_fs(F2FS_M_SB(mapping), true);
return 0;
-out_err:
- for (++i; i < cc->cluster_size; i++) {
- if (!cc->rpages[i])
- continue;
- redirty_page_for_writepage(wbc, cc->rpages[i]);
- unlock_page(cc->rpages[i]);
- }
- return err;
}
int f2fs_write_multi_pages(struct compress_ctx *cc,
--
2.25.1
^ permalink raw reply [flat|nested] 3+ messages in thread