lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Wed, 04 Nov 2020 08:42:36 +0100 From: Mike Galbraith <efault@....de> To: Gratian Crisan <gratian.crisan@...com>, Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org> Cc: linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org, Brandon Streiff <brandon.streiff@...com>, Ingo Molnar <mingo@...hat.com>, Darren Hart <dvhart@...radead.org>, James Minor <james.minor@...com>, Sebastian Andrzej Siewior <bigeasy@...utronix.de> Subject: Re: BUG_ON(!newowner) in fixup_pi_state_owner() On Wed, 2020-11-04 at 01:56 +0100, Mike Galbraith wrote: > On Tue, 2020-11-03 at 17:31 -0600, Gratian Crisan wrote: > > Hi all, > > > > I apologize for waking up the futex demons (and replying to my own > > email), but ... > > > > Gratian Crisan writes: > > > > > > Brandon and I have been debugging a nasty race that leads to > > > BUG_ON(!newowner) in fixup_pi_state_owner() in futex.c. So far > > > we've only been able to reproduce the issue on 4.9.y-rt kernels. > > > We are still testing if this is a problem for later RT branches. > > > > I was able to reproduce the BUG_ON(!newowner) in fixup_pi_state_owner() > > with a 5.10.0-rc1-rt1 kernel (currently testing 5.10.0-rc2-rt4). > > My box says it's generic. --- kernel/futex.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) --- a/kernel/futex.c +++ b/kernel/futex.c @@ -2383,7 +2383,18 @@ static int fixup_pi_state_owner(u32 __us * Since we just failed the trylock; there must be an owner. */ newowner = rt_mutex_owner(&pi_state->pi_mutex); - BUG_ON(!newowner); + + /* + * Why? Because I know what I'm doing with these beasts? Nope, + * but what the hell, a busy restart loop let f_boosted become + * owner, so go for it. Box still boots, works, no longer makes + * boom with fbomb_v2, and as an added bonus, didn't even blow + * futextests all up. Maybe it'll help... or not, we'll see. + */ + if (unlikely(!newowner)) { + err = -EAGAIN; + goto handle_err; + } } else { WARN_ON_ONCE(argowner != current); if (oldowner == current) {
Powered by blists - more mailing lists