On Mon, Aug 10, 2020 at 04:08:59PM -0400, Joel Fernandes wrote: > On Fri, Aug 07, 2020 at 03:20:15PM -0700, Paul E. McKenney wrote: > > On Fri, Aug 07, 2020 at 04:47:56PM -0400, Joel Fernandes wrote: > > > Hi, > > > Adding more of us working on RCU as well. Johan from another team at > > > Google discovered a likely issue in openswitch, details below: > > > > > > On Fri, Aug 7, 2020 at 11:32 AM Johan Knöös <jkn...@google.com> wrote: > > > > On Tue, Aug 4, 2020 at 8:52 AM Gregory Rose <gvrose8...@gmail.com> > > > > wrote: > > > > > On 8/3/2020 12:01 PM, Johan Knöös via discuss wrote: > > > > > > Hi Open vSwitch contributors, > > > > > > > > > > > > We have found openvswitch is causing double-freeing of memory. The > > > > > > issue was not present in kernel version 5.5.17 but is present in > > > > > > 5.6.14 and newer kernels. > > > > > > > > > > > > After reverting the RCU commits below for debugging, enabling > > > > > > slub_debug, lockdep, and KASAN, we see the warnings at the end of > > > > > > this > > > > > > email in the kernel log (the last one shows the double-free). When I > > > > > > revert 50b0e61b32ee890a75b4377d5fbe770a86d6a4c1 ("net: openvswitch: > > > > > > fix possible memleak on destroy flow-table"), the symptoms > > > > > > disappear. > > > > > > While I have a reliable way to reproduce the issue, I unfortunately > > > > > > don't yet have a process that's amenable to sharing. Please take a > > > > > > look. > > > > > > > > > > > > 189a6883dcf7 rcu: Remove kfree_call_rcu_nobatch() > > > > > > 77a40f97030b rcu: Remove kfree_rcu() special casing and > > > > > > lazy-callback handling > > > > > > e99637becb2e rcu: Add support for debug_objects debugging for > > > > > > kfree_rcu() > > > > > > 0392bebebf26 rcu: Add multiple in-flight batches of kfree_rcu() work > > > > > > 569d767087ef rcu: Make kfree_rcu() use a non-atomic ->monitor_todo > > > > > > a35d16905efc rcu: Add basic support for kfree_rcu() batching > > > > > > Note that these reverts were only for testing the same code, because > > > he was testing 2 different kernel versions. One of them did not have > > > this set. So I asked him to revert. There's no known bug in the > > > reverted code itself. But somehow these patches do make it harder for > > > him to reproduce the issue. > > > > Perhaps they adjust timing? > > Yes that could be it. In my testing (which is unrelated to OVS), the issue > happens only with TREE02. I can reproduce the issue in [1] on just boot-up of > TREE02. > > I could have screwed up something in my segcblist count patch, any hints > would be great. I'll dig more into it as well.
Has anyone taken a close look at 50b0e61b32ee ("net: openvswitch: fix possible memleak on destroy flow-table") commit? Maybe it avoided the memleak so thoroughly that it did a double free? Thanx, Paul > > > But then again, I have not heard reports of this warning firing. Paul, > > > has this come to your radar recently? > > > > I have not seen any recent WARNs in rcu_do_batch(). I am guessing that > > this is one of the last two in that function? > > > > If so, have you tried using CONFIG_DEBUG_OBJECTS_RCU_HEAD=y? That Kconfig > > option is designed to help locate double frees via RCU. > > Yes true, kfree_rcu() also has support for this. Jonathan, did you get a > chance to try this out in your failure scenario? > > thanks, > > - Joel > > [1] https://lore.kernel.org/lkml/20200720005334.GC19262@shao2-debian/ _______________________________________________ discuss mailing list disc...@openvswitch.org https://mail.openvswitch.org/mailman/listinfo/ovs-discuss