On 2024/5/15 12:42, Jaegeuk Kim wrote:
On 05/15, Chao Yu wrote:
On 2024/5/15 0:09, Jaegeuk Kim wrote:
On 05/10, Chao Yu wrote:
If lfs mode is on, buffered read may race w/ OPU dio write as below,
it may cause buffered read hits unwritten data unexpectly, and for
dio read, the race condition exists as well.
Thread A Thread B
- f2fs_file_write_iter
- f2fs_dio_write_iter
- __iomap_dio_rw
- f2fs_iomap_begin
- f2fs_map_blocks
- __allocate_data_block
- allocated blkaddr #x
- iomap_dio_submit_bio
- f2fs_file_read_iter
- filemap_read
- f2fs_read_data_folio
- f2fs_mpage_readpages
- f2fs_map_blocks
: get blkaddr #x
- f2fs_submit_read_bio
IRQ
- f2fs_read_end_io
: read IO on blkaddr #x complete
IRQ
- iomap_dio_bio_end_io
: direct write IO on blkaddr #x complete
This patch introduces a new per-inode i_opu_rwsem lock to avoid
such race condition.
Wasn't this supposed to be managed by user-land?
Actually, the test case is:
1. mount w/ lfs mode
2. touch file;
3. initialize file w/ 4k zeroed data; fsync;
4. continue triggering dio write 4k zeroed data to file;
5. and meanwhile, continue triggering buf/dio 4k read in file,
use md5sum to verify the 4k data;
It expects data is all zero, however it turned out it's not.
Can we check outstanding write bios instead of abusing locks?
I didn't figure out a way to solve this w/o lock, due to:
- write bios can be issued after outstanding write bios check condition,
result in the race.
- once read() detects that there are outstanding write bios, we need to
delay read flow rather than fail it, right? It looks using a lock is more
proper here?
Any suggestion?
Thanks,
Thanks,
Fixes: f847c699cff3 ("f2fs: allow out-place-update for direct IO in LFS mode")
Signed-off-by: Chao Yu <c...@kernel.org>
---
v2:
- fix to cover dio read path w/ i_opu_rwsem as well.
fs/f2fs/f2fs.h | 1 +
fs/f2fs/file.c | 28 ++++++++++++++++++++++++++--
fs/f2fs/super.c | 1 +
3 files changed, 28 insertions(+), 2 deletions(-)
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 30058e16a5d0..91cf4b3d6bc6 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -847,6 +847,7 @@ struct f2fs_inode_info {
/* avoid racing between foreground op and gc */
struct f2fs_rwsem i_gc_rwsem[2];
struct f2fs_rwsem i_xattr_sem; /* avoid racing between reading and
changing EAs */
+ struct f2fs_rwsem i_opu_rwsem; /* avoid racing between buf read and opu
dio write */
int i_extra_isize; /* size of extra space located in
i_addr */
kprojid_t i_projid; /* id for project quota */
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 72ce1a522fb2..4ec260af321f 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -4445,6 +4445,7 @@ static ssize_t f2fs_dio_read_iter(struct kiocb *iocb,
struct iov_iter *to)
const loff_t pos = iocb->ki_pos;
const size_t count = iov_iter_count(to);
struct iomap_dio *dio;
+ bool do_opu = f2fs_lfs_mode(sbi);
ssize_t ret;
if (count == 0)
@@ -4457,8 +4458,14 @@ static ssize_t f2fs_dio_read_iter(struct kiocb *iocb,
struct iov_iter *to)
ret = -EAGAIN;
goto out;
}
+ if (do_opu && !f2fs_down_read_trylock(&fi->i_opu_rwsem)) {
+ f2fs_up_read(&fi->i_gc_rwsem[READ]);
+ ret = -EAGAIN;
+ goto out;
+ }
} else {
f2fs_down_read(&fi->i_gc_rwsem[READ]);
+ f2fs_down_read(&fi->i_opu_rwsem);
}
/*
@@ -4477,6 +4484,7 @@ static ssize_t f2fs_dio_read_iter(struct kiocb *iocb,
struct iov_iter *to)
ret = iomap_dio_complete(dio);
}
+ f2fs_up_read(&fi->i_opu_rwsem);
f2fs_up_read(&fi->i_gc_rwsem[READ]);
file_accessed(file);
@@ -4523,7 +4531,13 @@ static ssize_t f2fs_file_read_iter(struct kiocb *iocb,
struct iov_iter *to)
if (f2fs_should_use_dio(inode, iocb, to)) {
ret = f2fs_dio_read_iter(iocb, to);
} else {
+ bool do_opu = f2fs_lfs_mode(F2FS_I_SB(inode));
+
+ if (do_opu)
+ f2fs_down_read(&F2FS_I(inode)->i_opu_rwsem);
ret = filemap_read(iocb, to, 0);
+ if (do_opu)
+ f2fs_up_read(&F2FS_I(inode)->i_opu_rwsem);
if (ret > 0)
f2fs_update_iostat(F2FS_I_SB(inode), inode,
APP_BUFFERED_READ_IO, ret);
@@ -4748,14 +4762,22 @@ static ssize_t f2fs_dio_write_iter(struct kiocb *iocb,
struct iov_iter *from,
ret = -EAGAIN;
goto out;
}
+ if (do_opu && !f2fs_down_write_trylock(&fi->i_opu_rwsem)) {
+ f2fs_up_read(&fi->i_gc_rwsem[READ]);
+ f2fs_up_read(&fi->i_gc_rwsem[WRITE]);
+ ret = -EAGAIN;
+ goto out;
+ }
} else {
ret = f2fs_convert_inline_inode(inode);
if (ret)
goto out;
f2fs_down_read(&fi->i_gc_rwsem[WRITE]);
- if (do_opu)
+ if (do_opu) {
f2fs_down_read(&fi->i_gc_rwsem[READ]);
+ f2fs_down_write(&fi->i_opu_rwsem);
+ }
}
/*
@@ -4779,8 +4801,10 @@ static ssize_t f2fs_dio_write_iter(struct kiocb *iocb,
struct iov_iter *from,
ret = iomap_dio_complete(dio);
}
- if (do_opu)
+ if (do_opu) {
+ f2fs_up_write(&fi->i_opu_rwsem);
f2fs_up_read(&fi->i_gc_rwsem[READ]);
+ }
f2fs_up_read(&fi->i_gc_rwsem[WRITE]);
if (ret < 0)
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index daf2c4dbe150..b4ed3b094366 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1428,6 +1428,7 @@ static struct inode *f2fs_alloc_inode(struct super_block
*sb)
init_f2fs_rwsem(&fi->i_gc_rwsem[READ]);
init_f2fs_rwsem(&fi->i_gc_rwsem[WRITE]);
init_f2fs_rwsem(&fi->i_xattr_sem);
+ init_f2fs_rwsem(&fi->i_opu_rwsem);
/* Will be used by directory only */
fi->i_dir_level = F2FS_SB(sb)->dir_level;
--
2.40.1
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