Hello Damien,
IIUC, you are trying to fix a stale data read by DIO read for the case
you explained in your patch w.r.t. DIO-write forced to write as buffIO.
Coincidentally I was just looking at the same code path just now.
So I do have a query to you/f2fs group. Below could be silly one, as I
don't understand F2FS in great detail.
How is the stale data by DIO read, is protected against a mmap
writes via f2fs_vm_page_mkwrite?
f2fs_vm_page_mkwrite() f2fs_direct_IO (read)
filemap_write_and_wait_range()
-> f2fs_get_blocks()
-> submit_bio()
-> set_page_dirty()
Is above race possible with current f2fs code?
i.e. f2fs_direct_IO could read the stale data from the blocks
which were allocated due to mmap fault?
Am I missing something here?
-ritesh
On 11/26/19 1:27 PM, Damien Le Moal wrote:
f2fs_preallocate_blocks() identifies direct IOs using the IOCB_DIRECT
flag for a kiocb structure. However, the file system direct IO handler
function f2fs_direct_IO() may have decided that a direct IO has to be
exececuted as a buffered IO using the function f2fs_force_buffered_io().
This is the case for instance for volumes including zoned block device
and for unaligned write IOs with LFS mode enabled.
These 2 different methods of identifying direct IOs can result in
inconsistencies generating stale data access for direct reads after a
direct IO write that is treated as a buffered write. Fix this
inconsistency by combining the IOCB_DIRECT flag test with the result
of f2fs_force_buffered_io().
Reported-by: Javier Gonzalez <javier@xxxxxxxxxxx>
Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
---
fs/f2fs/data.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 5755e897a5f0..8ac2d3b70022 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1073,6 +1073,8 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
int flag;
int err = 0;
bool direct_io = iocb->ki_flags & IOCB_DIRECT;
+ bool do_direct_io = direct_io &&
+ !f2fs_force_buffered_io(inode, iocb, from);
/* convert inline data for Direct I/O*/
if (direct_io) {
@@ -1081,7 +1083,7 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
return err;
}
- if (direct_io && allow_outplace_dio(inode, iocb, from))
+ if (do_direct_io && allow_outplace_dio(inode, iocb, from))
return 0;
if (is_inode_flag_set(inode, FI_NO_PREALLOC))
