On 11/16/2015 09:27 PM, Jeff Moyer wrote:
Hi Avi,
Avi Kivity <avi@xxxxxxxxxxxx> writes:
Due to a bug in my program, I initiated a read beyond
eof. Specifically, the file size is 13002 bytes and the read offset is
13312 (0x3400).
I would expect such a read to return 0 bytes read, but io_getevents
returns -310, which is suspiciously equal to (13002 - 13312).
I attach a reproducer.
4.2.5-201.fc22.x86_64
Are my expectations incorrect, or is this a bug in aio or xfs?
Your expectations are correct. The bug was introduced by commit
9fe55eea7e4b4 (Fix race when checking i_size on direct i/o read). I've
CC'd the patch author and linux-fsdevel. I'm not sure what the right
fix is, given that the size checks were removed from the vfs to fix some
race condition. Unfortunately, the commit message doesn't really do a
good job of explaining the race. In order to save others time, here is
a good explanation of the problem that commit is meant to fix, along
with a reproducer:
http://marc.info/?l=linux-fsdevel&m=138641356614458&w=2
Thanks for the great bug report, and sorry I have no solution to
proffer.
Thanks. I will await a fix with interest.
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