Am 30.09.2011 17:49, schrieb Amit Shah: > On (Fri) 30 Sep 2011 [16:23:30], Stefan Hajnoczi wrote: >> On Fri, Sep 30, 2011 at 12:27 PM, Amit Shah <amit.s...@redhat.com> wrote: >>> On (Fri) 30 Sep 2011 [11:39:11], Stefan Hajnoczi wrote: >>>> QED's metadata caching strategy allows two parallel requests to race for >>>> metadata lookup. The first one to complete will populate the metadata >>>> cache and the second one will drop the data it just read in favor of the >>>> cached data. >>>> >>>> There is a use-after-free in qed_read_l2_table_cb() and >>>> qed_commit_l2_update() where l2_table->offset was used after the >>>> l2_table may have been freed due to a metadata lookup race. Fix this by >>>> keeping the l2_offset in a local variable and not reaching into the >>>> possibly freed l2_table. >>>> >>>> Reported-by: Amit Shah <amit.s...@redhat.com> >>>> Signed-off-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com> >>>> --- >>>> Hi Amit, >>>> Thanks for reporting the assertion failure you saw at >>>> http://fpaste.org/CDuv/. >>>> Does this patch fix the problem? >>> >>> Yes, this fixes it. >> >> Were you able to reliably reproduce the assertion failure before? > > Absolutely. > > I even reverted the patch and tried the same image; same segfault > again. > >> I wonder because this only happens when two metadata lookups race >> (which is rare enough on my setup that I've never seen this failure). >> It might be worth trying a few times. > > Get the F16 beta-rc LXE live iso, install guest. It doesn't cleanly > reboot, you have to kill the VM. Next start of the VM produces this > segfault. > > https://alt.fedoraproject.org/pub/alt/stage/16-Beta.RC2/Live/x86_64/Fedora-16-Beta-x86_64-Live-LXDE.iso
Can we try to artificially produce it in a qemu-iotests case? Kevin
