Hi,
在 2022/3/15 16:04, Gao Xiang 写道:
Hi Xuenan,
(+ Cc Darrick.. )
On Tue, Mar 15, 2022 at 02:57:45PM +0800, Guo Xuenan wrote:
when get fiemap starting from MAX_LFS_FILESIZE, (maxbytes - *len) < start
will always true , then *len set zero. because of start offset is byhond
file size, for erofs filesystem it will always return iomap.length with
zero,iomap iterate will be infinite loop.
Thanks! If my understanding is correct, we once had a similar
behavior in compressed inodes and it has been worked around with
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/erofs/zmap.c?h=v5.17-rc8#n762
Yes, your understanding is accurate. But non-compressed inode,still has
the same problem, In my testcase,
set filemap start offset "0x7fffffffffffffff", filemap len will always
be reset to 0;
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/erofs/data.c?h=v5.17-rc8#n267
will always set iomap->length. But i don't think this is the problem of
erofs.
In my opinion, for this situation, when filemap len is 0, there is no
point to enter a specific filesystem.
Thanks!
But yeah, if iomap can define or handle post-EOF extent length
behavior exactly, it would be much better!
So on my side,
Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
(Also you might need to inform iomap maintainer Darrick as well..)
Thanks,
Gao Xiang
In order to avoid this situation, it is better to calculate the actual
mapping length at first. If the len is 0, there is no need to continue
the operation.
------------[ cut here ]------------
WARNING: CPU: 7 PID: 905 at fs/iomap/iter.c:35 iomap_iter+0x97f/0xc70
Modules linked in: xfs erofs
CPU: 7 PID: 905 Comm: iomap Tainted: G W 5.17.0-rc8 #27
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:iomap_iter+0x97f/0xc70
Code: 85 a1 fc ff ff e8 71 be 9c ff 0f 1f 44 00 00 e9 92 fc ff ff e8 62 be 9c ff 0f 0b b8 fb ff ff ff e9 fc f8 ff ff e8 51 be 9c ff <0f> 0b e9 2b fc ff ff e8 45 be 9c ff 0f 0b e9 e1 fb ff ff e8 39 be
RSP: 0018:ffff888060a37ab0 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff888060a37bb0 RCX: 0000000000000000
RDX: ffff88807e19a900 RSI: ffffffff81a7da7f RDI: ffff888060a37be0
RBP: 7fffffffffffffff R08: 0000000000000000 R09: ffff888060a37c20
R10: ffff888060a37c67 R11: ffffed100c146f8c R12: 7fffffffffffffff
R13: 0000000000000000 R14: ffff888060a37bd8 R15: ffff888060a37c20
FS: 00007fd3cca01540(0000) GS:ffff888108780000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020010820 CR3: 0000000054b92000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
iomap_fiemap+0x1c9/0x2f0
erofs_fiemap+0x64/0x90 [erofs]
do_vfs_ioctl+0x40d/0x12e0
__x64_sys_ioctl+0xaa/0x1c0
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xae
</TASK>
---[ end trace 0000000000000000 ]---
watchdog: BUG: soft lockup - CPU#7 stuck for 26s! [iomap:905]
Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Signed-off-by: Guo Xuenan <guoxuenan@xxxxxxxxxx>
---
fs/ioctl.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/fs/ioctl.c b/fs/ioctl.c
index 1ed097e94af2..7f70e90766ed 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -171,8 +171,6 @@ int fiemap_prep(struct inode *inode, struct fiemap_extent_info *fieinfo,
u32 incompat_flags;
int ret = 0;
- if (*len == 0)
- return -EINVAL;
if (start > maxbytes)
return -EFBIG;
@@ -182,6 +180,9 @@ int fiemap_prep(struct inode *inode, struct fiemap_extent_info *fieinfo,
if (*len > maxbytes || (maxbytes - *len) < start)
*len = maxbytes - start;
+ if (*len == 0)
+ return -EINVAL;
+
supported_flags |= FIEMAP_FLAG_SYNC;
supported_flags &= FIEMAP_FLAGS_COMPAT;
incompat_flags = fieinfo->fi_flags & ~supported_flags;
--
2.22.0
.
