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Tue, 06 Jul 2021 21:06:44 -0700 (PDT) Sender: Guenter Roeck Subject: Re: [tip: sched/core] sched/core: Initialize the idle task with preemption disabled To: Valentin Schneider , linux-kernel@vger.kernel.org Cc: linux-tip-commits@vger.kernel.org, Ingo Molnar , Peter Zijlstra , x86@kernel.org References: <20210512094636.2958515-1-valentin.schneider@arm.com> <162081815405.29796.14574924529325899839.tip-bot2@tip-bot2> <20210706194456.GA1823793@roeck-us.net> <87fswr6lqv.mognet@arm.com> From: Guenter Roeck Message-ID: <0d792e69-8ba3-5658-16ea-c1090bffa410@roeck-us.net> Date: Tue, 6 Jul 2021 21:06:40 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <87fswr6lqv.mognet@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/6/21 4:55 PM, Valentin Schneider wrote: > > Hi Guenter, > > On 06/07/21 12:44, Guenter Roeck wrote: >> This patch results in several messages similar to the following >> when booting s390 images in qemu. >> >> [ 1.690807] BUG: sleeping function called from invalid context at include/linux/percpu-rwsem.h:49 >> [ 1.690925] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: swapper/0 >> [ 1.691053] no locks held by swapper/0/1. >> [ 1.691310] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.13.0-11788-g79160a603bdb #1 >> [ 1.691469] Hardware name: QEMU 2964 QEMU (KVM/Linux) >> [ 1.691612] Call Trace: >> [ 1.691718] [<0000000000d98bb0>] show_stack+0x90/0xf8 >> [ 1.692040] [<0000000000da894c>] dump_stack_lvl+0x74/0xa8 >> [ 1.692134] [<0000000000187e52>] ___might_sleep+0x15a/0x170 >> [ 1.692228] [<000000000014f588>] cpus_read_lock+0x38/0xc0 >> [ 1.692320] [<0000000000182e8a>] smpboot_register_percpu_thread+0x2a/0x160 >> [ 1.692412] [<00000000014814b8>] cpuhp_threads_init+0x28/0x60 >> [ 1.692505] [<0000000001487a30>] smp_init+0x28/0x90 >> [ 1.692597] [<00000000014779a6>] kernel_init_freeable+0x1f6/0x270 >> [ 1.692689] [<0000000000db7466>] kernel_init+0x2e/0x160 >> [ 1.692779] [<0000000000103618>] __ret_from_fork+0x40/0x58 >> [ 1.692870] [<0000000000dc6e12>] ret_from_fork+0xa/0x30 >> >> Reverting this patch fixes the problem. >> Bisect log is attached. >> >> Guenter >> > > Thanks for the report. > > So somehow the init task ends up with a non-zero preempt_count()? Per > FORK_PREEMPT_COUNT we should exit __ret_from_fork() with a zero count, are > you hitting the WARN_ONCE() in finish_task_switch()? > > Does CONFIG_DEBUG_PREEMPT=y yield anything interesting? > My configuration doesn't have CONFIG_PREEMPT enabled. Guenter