Re: [PATCH] fix corruption case for block size < page size

[Lachlan McIlroy <lachlan@xxxxxxx>]

Eric Sandeen wrote:
> Lachlan McIlroy wrote:
> > Eric Sandeen wrote:
> > > Eric Sandeen wrote:
> > >
> > > > Gah; or not.  what is going on here...  Doing just steps 1, 2, 3, 4
> > > > (ending on the extending truncate):
> > > >
> > > > # xfs_io -c "pwrite -S 0x11 -b 4096 0 4096" -c "mmap -r 0 512" -c "mread
> > > > 0 512" -c "munmap" -c "truncate 256" -c "truncate 514" -t -d -f
> > > > /mnt/scratch/testfile
> > > >
> > > > # xfs_bmap -v /mnt/scratch/testfile
> > > > /mnt/scratch/testfile:
> > > >  EXT: FILE-OFFSET      BLOCK-RANGE      AG AG-OFFSET        TOTAL
> > > >    0: [0..0]:          63..63            0 (63..63)             1
> > > >    1: [1..1]:          hole                                     1
> > > >
> > > > It looks like what I expect, at this point.  But then:
> > > >
> > > > # sync
> > > > # xfs_bmap -v /mnt/scratch/testfile
> > > > /mnt/scratch/testfile:
> > > >  EXT: FILE-OFFSET      BLOCK-RANGE      AG AG-OFFSET        TOTAL
> > > >    0: [0..1]:          63..64            0 (63..64)             2
> > > >
> > > > Um, why'd that last block get mapped in?  mmap vs. direct IO I'm
> > > > guessing... w/o the mmap read this does not happen.
> > > Replying to myself twice?  I really need to go to bed.
> > >
> > > So this all does seem to come back to page_state_convert.
> > >
> > > Both the extending write in the original case and the sync above find
> > > their way there; but esp. in the sync test above, why do we have *any*
> > > work to do?
> > Eric, did you find out why sync was allocating that second block?
>
> I'm afraid this has been on the back burner (or maybe further back) for
> a while... so... either "no" or "I don't remember" :)

Just trying your test case.  It's not related to direct I/O or mmap I/O
since I can reproduce it without those.

# xfs_io -f -c "pwrite -S 0x11 -b 513 0 513" -c "truncate 1" -c "truncate 513" 
file
wrote 513/513 bytes at offset 0
513.000000 bytes, 1 ops; 0.0000 sec (8.895 MiB/sec and 18181.8182 ops/sec)
# xfs_bmap -vvp file; sync; xfs_bmap -vvp file
file:
 EXT: FILE-OFFSET      BLOCK-RANGE      AG AG-OFFSET        TOTAL FLAGS
   0: [0..0]:          48..48            0 (48..48)             1 00000
   1: [1..1]:          hole                                     1
 FLAG Values:
    010000 Unwritten preallocated extent
    001000 Doesn't begin on stripe unit
    000100 Doesn't end   on stripe unit
    000010 Doesn't begin on stripe width
    000001 Doesn't end   on stripe width
file:
 EXT: FILE-OFFSET      BLOCK-RANGE      AG AG-OFFSET        TOTAL FLAGS
   0: [0..1]:          48..49            0 (48..49)             2 00000
 FLAG Values:
    010000 Unwritten preallocated extent
    001000 Doesn't begin on stripe unit
    000100 Doesn't end   on stripe unit
    000010 Doesn't begin on stripe width
    000001 Doesn't end   on stripe width

xfs_bmap will cause the file to be flushed so there should be no dirty
data to be flushed during the sync.  Strange.