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 Amit