Re: LTP write03 writev07 xfs failures

[Brian Foster <bfoster@redhat.com>]

cc Christoph

On Mon, Feb 27, 2017 at 12:22:20PM +0800, Xiong Zhou wrote:
> Hi,
> 
> These 2 tests PASS on Linus tree commit:
>   37c8596 Merge tag 'tty-4.11-rc1' of git://git.kernel.org/pub/scm/linux...
> FAIL on commit:
>   60e8d3e Merge tag 'pci-v4.11-changes' of git://git.kernel.org/pub/scm/...
> 
> LTP latest commit: c60d3ca move_pages12: include lapi/mmap.h
> 
> Steps:
> 
> sh-4.2# pwd
> /root/ltp
> sh-4.2# git log --oneline -1
> c60d3ca move_pages12: include lapi/mmap.h
> sh-4.2# uname -r
> 4.10.0-master-60e8d3e+
> sh-4.2# mount | grep test1
> /dev/sda3 on /test1 type xfs (rw,relatime,seclabel,attr2,inode64,logbsize=256k,sunit=512,swidth=512,noquota)
> sh-4.2# xfs_info /test1
> meta-data=/dev/sda3              isize=512    agcount=16, agsize=245696 blks
>          =                       sectsz=512   attr=2, projid32bit=1
>          =                       crc=1        finobt=1 spinodes=0
> data     =                       bsize=4096   blocks=3931136, imaxpct=25
>          =                       sunit=64     swidth=64 blks
> naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
> log      =internal               bsize=4096   blocks=2560, version=2
>          =                       sectsz=512   sunit=64 blks, lazy-count=1
> realtime =none                   extsz=4096   blocks=0, rtextents=0
> sh-4.2# 
> sh-4.2# TMPDIR=/test1 ./testcases/kernel/syscalls/write/write03
> write03     0  TINFO  :  Enter Block 1: test to check if write corrupts the file when write fails
> write03     1  TFAIL  :  write03.c:125: failure of write(2) corrupted the file
> write03     0  TINFO  :  Exit block 1
> sh-4.2# 

On a quick test, both of these are reproduced after commit fa7f138ac4
("xfs: clear delalloc and cache on buffered write failure"). That patch
fixed a problem where if the write allocates a block but fails to write
anything (written == 0), we'd leave a delalloc block lingering in the
inode.

With that change, this test now fails because it sends two writes within
a single block. The first allocates the block, writes 100 bytes and
returns successfully. The next attempts to write the next 100 bytes,
fails and triggers the cleanup of the block because we can't tell
whether this write or the previous had allocated it.

I'm not convinced the right solution is to just go back to the previous
code. That obviously reintroduces the original problem, but we'd also
still have a similar problem if the second (failed) write was a rewrite
of the first. The error handling of the second write would kill off the
blocks allocated and written to successfully by the first. I'm wondering
if the right thing to do here is factor in i_size as it appears that's
what this code did prior to the iomap transition. I'm not sure where
that leaves us wrt to writes into sparse files, though. I may need to
play with this a bit..

Christoph, any thoughts on this?

Brian

> sh-4.2# TMPDIR=/test1 ./testcases/kernel/syscalls/writev/writev07
> tst_test.c:760: INFO: Timeout per run is 0h 05m 00s
> writev07.c:60: INFO: starting test with initial file offset: 0 
> writev07.c:82: INFO: got EFAULT
> writev07.c:87: FAIL: file was written to
> writev07.c:93: PASS: offset stayed unchanged
> writev07.c:60: INFO: starting test with initial file offset: 65 
> writev07.c:82: INFO: got EFAULT
> writev07.c:89: PASS: file stayed untouched
> writev07.c:93: PASS: offset stayed unchanged
> writev07.c:60: INFO: starting test with initial file offset: 4096 
> writev07.c:82: INFO: got EFAULT
> writev07.c:89: PASS: file stayed untouched
> writev07.c:93: PASS: offset stayed unchanged
> writev07.c:60: INFO: starting test with initial file offset: 4097 
> writev07.c:82: INFO: got EFAULT
> writev07.c:89: PASS: file stayed untouched
> writev07.c:93: PASS: offset stayed unchanged
> 
> Summary:
> passed   7
> failed   1
> skipped  0
> warnings 0
> sh-4.2# 
> sh-4.2# mkfs.xfs -V
> mkfs.xfs version 4.7.0
> sh-4.2# cd ../xfsprogs/
> sh-4.2# git log --oneline -1
> d7e1f5f xfsprogs: Release v4.7
> sh-4.2# 
> 
> Thanks,
> Xiong
> --
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