Jan Kara <jack@xxxxxxx> writes: > On Thu 23-11-23 12:37:03, Ritesh Harjani wrote: >> Jan Kara <jack@xxxxxxx> writes: >> >> > The syzbot has reported that it can hit the warning in >> > ext4_dio_write_end_io() because i_size < i_disksize. Indeed the >> > reproducer creates a race between DIO IO completion and truncate >> > expanding the file and thus ext4_dio_write_end_io() sees an inconsistent >> > inode state where i_disksize is already updated but i_size is not >> > updated yet. Since we are careful when setting up DIO write and consider >> > it extending (and thus performing the IO synchronously with i_rwsem held >> > exclusively) whenever it goes past either of i_size or i_disksize, we >> > can use the same test during IO completion without risking entering >> > ext4_handle_inode_extension() without i_rwsem held. This way we make it >> > obvious both i_size and i_disksize are large enough when we report DIO >> > completion without relying on unreliable WARN_ON. >> >> Does it make sense to add this in ext4_handle_inode_extension()? >> WARN_ON_ONCE(!inode_is_locked(inode)); >> Ohk, we already have "lockdep_assert_held_write(&inode->i_rwsem)" so >> hopefully it can catch via lockdep. > > Exactly. > >> So, IIUC, the WARN happened when we were doing a non-extending >> AIO-DIO write which was racing with truncate trying to expand the file >> size. Because only then the DIO completion will not have i_rwsem held >> which can race with truncate. Truncate since it is expanding the file >> size, will not use inode_dio_wait() (since no block allocations). >> >> Is this understanding correct? > > Yes, correct. Thanks Jan, Also ext4_inode_extension_cleanup() function can take care of deleting the inode from the orphan list in case if there is a race with truncate which extended made both i_disksize and inode->i_size and the DIO completion couldn't call ext4_handle_inode_extension(), right? In that case, does it make sense to update a comment here too? @@ -350,7 +350,10 @@ static void ext4_inode_extension_cleanup(struct inode *inode, ssize_t count) } /* * If i_disksize got extended due to writeback of delalloc blocks while - * the DIO was running we could fail to cleanup the orphan list in + * the DIO was running, or + * If i_disksize and inode->i_size both got extened during truncate + * which raced with DIO completion, + * In both such cases, we could fail to cleanup the orphan list in * ext4_handle_inode_extension(). Do it now. */ if (!list_empty(&EXT4_I(inode)->i_orphan) && inode->i_nlink) { -ritesh > > Honza > >> >> > >> > Reported-by: syzbot+47479b71cdfc78f56d30@xxxxxxxxxxxxxxxxxxxxxxxxx >> > Fixes: 91562895f803 ("ext4: properly sync file size update after O_SYNC direct IO") >> > Signed-off-by: Jan Kara <jack@xxxxxxx> >> > --- >> > fs/ext4/file.c | 7 ++++--- >> > 1 file changed, 4 insertions(+), 3 deletions(-) >> > >> > diff --git a/fs/ext4/file.c b/fs/ext4/file.c >> > index 0166bb9ca160..ba497aabdd1e 100644 >> > --- a/fs/ext4/file.c >> > +++ b/fs/ext4/file.c >> > @@ -386,10 +386,11 @@ static int ext4_dio_write_end_io(struct kiocb *iocb, ssize_t size, >> > * blocks. But the code in ext4_iomap_alloc() is careful to use >> > * zeroed/unwritten extents if this is possible; thus we won't leave >> > * uninitialized blocks in a file even if we didn't succeed in writing >> > - * as much as we intended. >> > + * as much as we intended. Also we can race with truncate or write >> > + * expanding the file so we have to be a bit careful here. >> > */ >> > - WARN_ON_ONCE(i_size_read(inode) < READ_ONCE(EXT4_I(inode)->i_disksize)); >> > - if (pos + size <= READ_ONCE(EXT4_I(inode)->i_disksize)) >> > + if (pos + size <= READ_ONCE(EXT4_I(inode)->i_disksize) && >> > + pos + size <= i_size_read(inode)) >> > return size; >> > return ext4_handle_inode_extension(inode, pos, size); >> > } >> > -- >> > 2.35.3 >> > -- > Jan Kara <jack@xxxxxxxx> > SUSE Labs, CR