Re: [PATCH] ext4: Add support for data=alloc_on_commit mode

[Eric Sandeen <sandeen@redhat.com>]

Eric Sandeen wrote:
> Theodore Ts'o wrote:
>> Add an ext3 bug-for-bug compatible analogue for data=ordered mode.  In
>> this mode, we force all delayed allocation blocks involved with the
>> to-be-commited transaction to be allocated, and then flushed out to
>> disk before the transaction is commited.
>>
>> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> 
> Haven't really looked into the cause yet but I was playing with this,
> and ran:
> 
> # rm -f bigfile smallfile; dd if=/dev/zero of=bigfile bs=1M count=8192;
> echo boo > smallfile; time /root/fsync smallfile; time /root/fsync bigfile
> 
> which resulted in:
> 
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000060
> IP: [<ffffffffa02a6de1>] alloc_on_commit_callback+0x27/0x7f [ext4]

This may have been user error ... ignore for now, I'll follow up if I
decide it's real.  :)

-Eric