Messages in this thread | | | Date | Wed, 30 Jun 2021 14:21:05 +0200 | From | Steffen Klassert <> | Subject | Re: [PATCH] xfrm: Fix RCU vs hash_resize_mutex lock inversion |
| |
On Wed, Jun 30, 2021 at 02:11:24PM +0200, Varad Gautam wrote: > On 6/30/21 8:57 AM, Steffen Klassert wrote: > > On Mon, Jun 28, 2021 at 03:34:28PM +0200, Frederic Weisbecker wrote: > >> xfrm_bydst_resize() calls synchronize_rcu() while holding > >> hash_resize_mutex. But then on PREEMPT_RT configurations, > >> xfrm_policy_lookup_bytype() may acquire that mutex while running in an > >> RCU read side critical section. This results in a deadlock. > >> > >> In fact the scope of hash_resize_mutex is way beyond the purpose of > >> xfrm_policy_lookup_bytype() to just fetch a coherent and stable policy > >> for a given destination/direction, along with other details. > >> > >> The lower level net->xfrm.xfrm_policy_lock, which among other things > >> protects per destination/direction references to policy entries, is > >> enough to serialize and benefit from priority inheritance against the > >> write side. As a bonus, it makes it officially a per network namespace > >> synchronization business where a policy table resize on namespace A > >> shouldn't block a policy lookup on namespace B. > >> > >> Fixes: 77cc278f7b20 (xfrm: policy: Use sequence counters with associated lock) > >> Cc: stable@vger.kernel.org > >> Cc: Ahmed S. Darwish <a.darwish@linutronix.de> > >> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> > >> Cc: Varad Gautam <varad.gautam@suse.com> > >> Cc: Steffen Klassert <steffen.klassert@secunet.com> > >> Cc: Herbert Xu <herbert@gondor.apana.org.au> > >> Cc: David S. Miller <davem@davemloft.net> > >> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> > > > > Your patch has a conflicht with ("commit d7b0408934c7 xfrm: policy: Read > > seqcount outside of rcu-read side in xfrm_policy_lookup_bytype") > > from Varad. Can you please rebase onto the ipsec tree? > > > > Btw. Varad, your above mentioned patch tried to fix the same issue. > > Do we still need it, or is it obsolete with the fix from Frederic? > > > > The patch "xfrm: policy: Read seqcount outside of rcu-read side in > xfrm_policy_lookup_bytype" shouldn't be needed after Frederic's fix since > the offending mutex is now gone. It can be dropped.
Ok, so I'll revert your patch and apply Frederic's patch on top of that revert.
Thanks a lot everyone!
| |