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 PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Tue, 10 Aug 2021 22:38:30 +0200 From: Thomas Gleixner <tglx@...utronix.de> To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Clark Williams <williams@...hat.com> Cc: Steven Rostedt <rostedt@...dmis.org>, Dmitry Vyukov <dvyukov@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org Subject: Re: [PATCH PREEMPT_RT] kcov: fix locking splat from kcov_remote_start() On Tue, Aug 10 2021 at 11:50, Sebastian Andrzej Siewior wrote: > On 2021-08-09 15:59:09 [-0500], Clark Williams wrote: >> Saw the following splat on 5.14-rc4-rt5 with: > … >> Change kcov_remote_lock from regular spinlock_t to raw_spinlock_t so that >> we don't get "sleeping function called from invalid context" on PREEMPT_RT kernel. > > I'm not entirely happy with that: > - kcov_remote_start() decouples spin_lock_irq() and does local_irq_save() > + spin_lock() which shouldn't be done as per > Documentation/locking/locktypes.rst > I would prefer to see the local_irq_save() replaced by > local_lock_irqsave() so we get a context on what is going on. Which does not make it raw unless we create a raw_local_lock. > - kcov_remote_reset() has a kfree() with that irq-off lock acquired. That free needs to move out obviously > - kcov_remote_add() has a kmalloc() and is invoked with that irq-off > lock acquired. So does the kmalloc. > - kcov_remote_area_put() uses INIT_LIST_HEAD() for no reason (just > happen to notice). > > - kcov_remote_stop() does local_irq_save() + spin_lock(&kcov->lock);. > This should also create a splat. > > - With lock kcov_remote_lock acquired there is a possible > hash_for_each_safe() and list_for_each() iteration. I don't know what > the limits are here but with a raw_spinlock_t it will contribute to > the maximal latency. And that matters because? kcov has a massive overhead and with that enabled you care as much about latencies as you do when running with lockdep enabled. Thanks, tglx
Powered by blists - more mailing lists