Messages in this thread Patch in this message | | | Date | Tue, 15 Mar 2022 16:59:51 +0800 | Subject | Re: [PATCH] iomap: fix an infinite loop in iomap_fiemap | From | Guo Xuenan <> |
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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@linux.alibaba.com> > > (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@huawei.com> >> Signed-off-by: Guo Xuenan <guoxuenan@huawei.com> >> --- >> 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 > .
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