On Fri, Mar 18, 2022 at 03:21:23PM +0800, Guo Xuenan wrote: > Hi Darrick, > > 在 2022/3/18 6:05, Darrick J. Wong wrote: > > 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. > > > > > > 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; > > Looks fine to me (and I don't even really mind pulling this in) but this > > isn't a patch to fs/iomap/ -- doesn't the same issue potentially affect > > the fiemap implementations that do not use iomap? > > > > Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx> > > > > --D > > Thanks Darrick, you're right,there is something wrong with my statement. In > a strict sense, this modification here does not belong to fs/iomap, i can > change it to fs/vfs in v2 :) I have looked into the code of those > filesystem(btrfs,ext4,f2fs,nilfs2,ntfs3..) which don't use iomap, and did > some test. when start=0x7fffffffffffffff, and len = 0; btrfs: while len==0, > return -EINVAL directly; ext4: ext4_get_es_cache->ext4_fiemap_check_ranges, > return -EFBIG; f2fs: return -EFBIG; nilfs2: while len==0, do nothing and > return 0; ntfs3: return -EFBIG directly; so, as far as i can see, just > return -EINVAL earlyier in fiemap_prep has no side effect. It's dangerous for patch reviewers to think more about patches. :) But-- thinking further, why do we return EINVAL for a query length of zero? Why doesn't FIEMAP set fi_extents_mapped = 0 and return immediately? Oh, right, because the documentation (a) doesn't say much about return codes and (b) the current implementation returns *some* error code (EINVAL or EFBIG), so now people probably expect that. That said ... I think "File too large" is a more appropriate message than "Invalid argument" for when we truncated the request to maxbytes but then ended up with a zero-length request. Does changing the check at the top of the function to: if (*len == 0) return -EINVAL; if (start >= maxbytes) return -EFBIG; Cover this infinite loop case? (Admittedly, it is Sunday morning and the parts of my brain that handle integer rollover issues are still asleep.) --D > > Thanks. > > > > + > > > supported_flags |= FIEMAP_FLAG_SYNC; > > > supported_flags &= FIEMAP_FLAGS_COMPAT; > > > incompat_flags = fieinfo->fi_flags & ~supported_flags; > > > -- > > > 2.22.0 > > > > > .
