On Mon, Jul 25, 2022 at 11:20:50AM +0800, Li Jinlin wrote:
> I got an infinite loop and a WARNING report when executing a tail command
> in virtiofs.
>
> WARNING: CPU: 10 PID: 964 at fs/iomap/iter.c:34 iomap_iter+0x3a2/0x3d0
> Modules linked in:
> CPU: 10 PID: 964 Comm: tail Not tainted 5.19.0-rc7
> Call Trace:
> <TASK>
> dax_iomap_rw+0xea/0x620
> ? __this_cpu_preempt_check+0x13/0x20
> fuse_dax_read_iter+0x47/0x80
> fuse_file_read_iter+0xae/0xd0
> new_sync_read+0xfe/0x180
> ? 0xffffffff81000000
> vfs_read+0x14d/0x1a0
> ksys_read+0x6d/0xf0
> __x64_sys_read+0x1a/0x20
> do_syscall_64+0x3b/0x90
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> The tail command will call read() with a count of 0. In this case,
> iomap_iter() will report this WARNING, and always return 1 which casuing
> the infinite loop in dax_iomap_rw().
>
> Fixing by checking count whether is 0 in dax_iomap_rw().
>
> Fixes: ca289e0b95af ("fsdax: switch dax_iomap_rw to use iomap_iter")
> Signed-off-by: Li Jinlin <lijinlin3@xxxxxxxxxx>
Huh, I didn't know FUSE supports DAX and iomap now...
> ---
> fs/dax.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 4155a6107fa1..7ab248ed21aa 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1241,6 +1241,9 @@ dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
> loff_t done = 0;
> int ret;
>
> + if (!iomi.len)
> + return 0;
Hmm, most of the callers of dax_iomap_rw skip the whole call if
iov_iter_count(to)==0, so I wonder if fuse_dax_read_iter should do the
same?
That said, iomap_dio_rw bails early if you pass it iomi.len, so I don't
have any real objections to this.
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
> +
> if (iov_iter_rw(iter) == WRITE) {
> lockdep_assert_held_write(&iomi.inode->i_rwsem);
> iomi.flags |= IOMAP_WRITE;
> --
> 2.30.2
>
