From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Guilherme G. Piccoli" Subject: [PATCH 05/30] misc/pvpanic: Convert regular spinlock into trylock on panic path Date: Wed, 27 Apr 2022 19:48:59 -0300 Message-ID: <20220427224924.592546-6-gpiccoli@igalia.com> References: <20220427224924.592546-1-gpiccoli@igalia.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=bjmQBon4ZPf54pX5Of0jL1twDGChrxI7tbY8kSwcQmQ=; b=KPbYGPRmNMOeJr 441MpiDemJuEgTyVZGDGluRgV3l1ger26QHB9a++DV+BFQOAz6LhSxGUmtBvl2SoyjlV9Un4VY3EZ zzgGKhNv3XEOlU8DBwo5iIkUXwiKw2Xh7rJbDnOZM6oxXC9+G9a7yxZQyOhkc3kYQx+8LMJacTCsi 3O4wKp6WHtVpmkB/PkIEwnmGgKqSLEvjaYU3JDuLGpYRuiqAKU3kC9h8mQJrJfTI5PB19OMqeuKHn LE200hvY13gAVh/i+pdCSO7NP8M/ODhAuQ067rNl4Q6CgOq9O4//O7BVsUJ8E3KEqo5rAyzjJIld1 q0qyiJYZYVD/+vum3DDg==; DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Sender:Reply-To:Content-Type:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=/X9VGFpkqSi0Xw+sb2fnqT5ti0fEX/+xmh5q7q7MhDY=; b=p3QOIFADQeeHCVp8bxPKwO62s+ EGcZOVKN2qbhBt1Pf/EZXw+tkBx2x9DRVMO1uTp94JqIADubO77jiICP/E04L/nn99FEYBzZb+44L /kz24xVDrX4FFqomkvxzWUTFlHhE4ZhZCfkHWBQr0/Lzkqr3CE/w4r7fAtX83L8f0pEarK5Qx6XYH 4zbdyCjIZQkKS6mh2t53k79tPqORut15Ek94GDPyIzx6i+d57M9a0UcH7EVEXkkbVPk2r+5s4ram2 N0+1/N2WpK9qFZ8QFj+vJFSqHIZNJD4YgbbIqqLYxl+DJIQthPO2tybUvOHdIFVD8Tw3e7+DHlkve LuLH0yww==; In-Reply-To: <20220427224924.592546-1-gpiccoli@igalia.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-um" Errors-To: linux-um-bounces+glud-user-mode-linux-devel=m.gmane-mx.org@lists.infradead.org To: akpm@linux-foundation.org, bhe@redhat.com, pmladek@suse.com, kexec@lists.infradead.org Cc: linux-kernel@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com, coresight@lists.linaro.org, linuxppc-dev@lists.ozlabs.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-edac@vger.kernel.org, linux-hyperv@vger.kernel.org, linux-leds@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linux-pm@vger.kernel.org, linux-remoteproc@vger.kernel.org, linux-s390@vger.kernel.org, linux-tegra@vger.kernel.org, linux-um@lists.infradead.org, linux-xtensa@linux-xtensa.org, netdev@vger.kernel.org, openipmi-developer@lists.sourceforge.net, rcu@vger.kernel.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org, kernel-dev@igalia.com, gpiccoli@igalia.com, kernel@gpiccoli.net, halves@canonical.com, fabiomirmar@gmail.com, alejandro.j.jimenez@oracle.com, andriy.shevchenko@linux.intel.com, arnd@arndb.de, bp@alien8. The pvpanic driver relies on panic notifiers to execute a callback on panic event. Such function is executed in atomic context - the panic function disables local IRQs, preemption and all other CPUs that aren't running the panic code. With that said, it's dangerous to use regular spinlocks in such path, as introduced by commit b3c0f8774668 ("misc/pvpanic: probe multiple instances"). This patch fixes that by replacing regular spinlocks with the trylock safer approach. It also fixes an old comment (about a long gone framebuffer code) and the notifier priority - we should execute hypervisor notifiers early, deferring this way the panic action to the hypervisor, as expected by the users that are setting up pvpanic. Fixes: b3c0f8774668 ("misc/pvpanic: probe multiple instances") Cc: Christophe JAILLET Cc: Mihai Carabas Cc: Shile Zhang Cc: Wang ShaoBo Cc: zhenwei pi Signed-off-by: Guilherme G. Piccoli --- drivers/misc/pvpanic/pvpanic.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/misc/pvpanic/pvpanic.c b/drivers/misc/pvpanic/pvpanic.c index 4b8f1c7d726d..049a12006348 100644 --- a/drivers/misc/pvpanic/pvpanic.c +++ b/drivers/misc/pvpanic/pvpanic.c @@ -34,7 +34,9 @@ pvpanic_send_event(unsigned int event) { struct pvpanic_instance *pi_cur; - spin_lock(&pvpanic_lock); + if (!spin_trylock(&pvpanic_lock)) + return; + list_for_each_entry(pi_cur, &pvpanic_list, list) { if (event & pi_cur->capability & pi_cur->events) iowrite8(event, pi_cur->base); @@ -55,9 +57,13 @@ pvpanic_panic_notify(struct notifier_block *nb, unsigned long code, void *unused return NOTIFY_DONE; } +/* + * Call our notifier very early on panic, deferring the + * action taken to the hypervisor. + */ static struct notifier_block pvpanic_panic_nb = { .notifier_call = pvpanic_panic_notify, - .priority = 1, /* let this called before broken drm_fb_helper() */ + .priority = INT_MAX, }; static void pvpanic_remove(void *param) -- 2.36.0