From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 710E911719 for ; Thu, 21 Dec 2023 22:35:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="SKgaKrQf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C4550C433C9; Thu, 21 Dec 2023 22:35:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1703198149; bh=ZeIqwSSwoulvkDcUFKITqFbriGraYgZwcNW31joyIeQ=; h=Date:To:From:Subject:From; b=SKgaKrQfbnzqQtB7HPvKDG3GEcpwY9CtxVHfJ2s0ZMpIrimpIySrUA6DctCWxwZsW coUNFcuiYKllJgVa8WzlaiCYQNGbgPfFdVtOr+pbBdYXgtF0gKynPUJfwuKl78xO6z 9GQbZpqs4LEjqxFOXnq4hUfy6SILGKi4en486i6c= Date: Thu, 21 Dec 2023 14:35:49 -0800 To: mm-commits@vger.kernel.org,pmladek@suse.com,lizhe.67@bytedance.com,lecopzer.chen@mediatek.com,kernelfans@gmail.com,john.ogness@linutronix.de,dianders@chromium.org,akpm@linux-foundation.org From: Andrew Morton Subject: + watchdog-softlockup-use-printk_cpu_sync_get_irqsave-to-serialize-reporting.patch added to mm-nonmm-unstable branch Message-Id: <20231221223549.C4550C433C9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: watchdog/softlockup: use printk_cpu_sync_get_irqsave() to serialize reporting has been added to the -mm mm-nonmm-unstable branch. Its filename is watchdog-softlockup-use-printk_cpu_sync_get_irqsave-to-serialize-reporting.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/watchdog-softlockup-use-printk_cpu_sync_get_irqsave-to-serialize-reporting.patch This patch will later appear in the mm-nonmm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Douglas Anderson Subject: watchdog/softlockup: use printk_cpu_sync_get_irqsave() to serialize reporting Date: Wed, 20 Dec 2023 13:15:35 -0800 Instead of introducing a spinlock, use printk_cpu_sync_get_irqsave() and printk_cpu_sync_put_irqrestore() to serialize softlockup reporting. Alone this doesn't have any real advantage over the spinlock, but this will allow us to use the same function in a future change to also serialize hardlockup crawls. NOTE: for the most part this serialization is important because we often end up in the show_regs() path and that has no built-in serialization if there are multiple callers at once. However, even in the case where we end up in the dump_stack() path this still has some advantages because the stack will be guaranteed to be together in the logs with the lockup message with no interleaving. NOTE: the fact that printk_cpu_sync_get_irqsave() is allowed to be called multiple times on the same CPU is important here. Specifically we hold the "lock" while calling dump_stack() which also gets the same "lock". This is explicitly documented to be OK and means we don't need to introduce a variant of dump_stack() that doesn't grab the lock. Link: https://lkml.kernel.org/r/20231220131534.2.Ia5906525d440d8e8383cde31b7c61c2aadc8f907@changeid Signed-off-by: Douglas Anderson Cc: John Ogness Cc: Lecopzer Chen Cc: Li Zhe Cc: Petr Mladek Cc: Pingfan Liu Signed-off-by: Andrew Morton --- kernel/watchdog.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/kernel/watchdog.c~watchdog-softlockup-use-printk_cpu_sync_get_irqsave-to-serialize-reporting +++ a/kernel/watchdog.c @@ -454,7 +454,7 @@ static enum hrtimer_restart watchdog_tim struct pt_regs *regs = get_irq_regs(); int duration; int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace; - static DEFINE_SPINLOCK(watchdog_output_lock); + unsigned long flags; if (!watchdog_enabled) return HRTIMER_NORESTART; @@ -521,7 +521,7 @@ static enum hrtimer_restart watchdog_tim /* Start period for the next softlockup warning. */ update_report_ts(); - spin_lock(&watchdog_output_lock); + printk_cpu_sync_get_irqsave(flags); pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n", smp_processor_id(), duration, current->comm, task_pid_nr(current)); @@ -531,7 +531,7 @@ static enum hrtimer_restart watchdog_tim show_regs(regs); else dump_stack(); - spin_unlock(&watchdog_output_lock); + printk_cpu_sync_put_irqrestore(flags); if (softlockup_all_cpu_backtrace) { trigger_allbutcpu_cpu_backtrace(smp_processor_id()); _ Patches currently in -mm which might be from dianders@chromium.org are watchdog-hardlockup-adopt-softlockup-logic-avoiding-double-dumps.patch watchdog-softlockup-use-printk_cpu_sync_get_irqsave-to-serialize-reporting.patch watchdog-hardlockup-use-printk_cpu_sync_get_irqsave-to-serialize-reporting.patch watchdog-if-panicking-and-we-dumped-everything-dont-re-enable-dumping.patch