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, 16 Jan 2019 12:50:42 +0000 From: Valentin Schneider <valentin.schneider@....com> To: Ingo Molnar <mingo@...nel.org>, linux-kernel <linux-kernel@...r.kernel.org> Cc: Peter Zijlstra <peterz@...radead.org>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Mark Rutland <mark.rutland@....com>, Julien Thierry <julien.thierry@....com> Subject: preempt_schedule_irq() loop question Hi, I've been wandering around preempt_schedule_irq() in sched/core.c, and got curious regarding how the arch code calls it. The main part of preempt_schedule_irq() is: do { preempt_disable(); local_irq_enable(); __schedule(true); local_irq_disable(); sched_preempt_enable_no_resched(); } while (need_resched()); Yet all the arch entry.S I looked at (I stopped after arm64, arm, x86_32, MIPS, powerpc) wrap the call to preempt_schedule_irq() in another do { ... } while (need_resched()) For instance, this is what's done in arm64: 1: bl preempt_schedule_irq // irq en/disable is done inside ldr x0, [tsk, #TSK_TI_FLAGS] // get new tasks TI_FLAGS tbnz x0, #TIF_NEED_RESCHED, 1b // needs rescheduling? I naively thought this could be attributed to something like preempt_schedule_irq() historically not having an inner loop, but it seems to have been there since the beginning of time (or at least up to the point where the git history stops). I don't see why we need to have these nested loops - AFAICT the one in preempt_schedule_irq() would suffice. What am I missing?
Powered by blists - more mailing lists