[Bug 15579] ext4 -o discard produces incorrect blocks of zeroes in newly created files under heavy read+truncate+append-new-file load

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https://bugzilla.kernel.org/show_bug.cgi?id=15579


Eric Sandeen <sandeen@redhat.com> changed:

           What    |Removed                     |Added
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                 CC|                            |sandeen@redhat.com




--- Comment #4 from Eric Sandeen <sandeen@redhat.com>  2010-03-22 21:40:52 ---
Just for what it's worth, I've had trouble reproducing this on another brand of
SSD... something like this (don't let the xfs_io throw you; it's just a
convenient way to generate the IO).  I did this on a 512M filesystem.

#!/bin/bash

SCRATCH_MNT=/mnt/scratch

rm -f $SCRATCH_MNT/*
touch $SCRATCH_MNT/outputfile

# Create several large-ish files
for I in `seq 1 240`; do
  xfs_io -F -f -c "pwrite 0 2m" $SCRATCH_MNT/file$I &>/dev/null
done

# reread the last bit of each, just for kicks, and truncate off 1m
for I in `seq 1 240`; do
  xfs_io -F -c "pread 1m 2m" $SCRATCH_MNT/file$I &>/dev/null
  xfs_io -F -c "truncate 1m" $SCRATCH_MNT/file$I
done

# Append the outputfile
xfs_io -F -c "pwrite 0 250m" $SCRATCH_MNT/outputfile &>/dev/null

In the end I don't get any corruption.  I was hoping to write a testcase for
this (one that didn't take 250G) :)

Does the above reflect your use case?  Does the above corrupt the outputfile on
your filesystem?  (note the "rm -rf" above, careful with that).  You could
substitute dd for xfs_io without much trouble if desired.

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