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Wed, 03 Jun 2026 11:56:36 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay05.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 653BuXKn49152280 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 3 Jun 2026 11:56:33 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4283E20040; Wed, 3 Jun 2026 11:56:33 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 52C0420043; Wed, 3 Jun 2026 11:56:31 +0000 (GMT) Received: from [9.124.223.153] (unknown [9.124.223.153]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 3 Jun 2026 11:56:31 +0000 (GMT) Message-ID: Date: Wed, 3 Jun 2026 17:26:30 +0530 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] powerpc/entry: Disable interrupts before irqentry_exit To: Peter Zijlstra Cc: maddy@linux.ibm.com, linuxppc-dev@lists.ozlabs.org, tglx@kernel.org, christophe.leroy@csgroup.eu, linux-kernel@vger.kernel.org, venkat88@linux.ibm.com, mkchauras@gmail.com References: <20260603095521.198267-1-sshegde@linux.ibm.com> <20260603101155.GV3493090@noisy.programming.kicks-ass.net> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <20260603101155.GV3493090@noisy.programming.kicks-ass.net> Content-Type: text/plain; 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Thanks for taking a look at it. On 6/3/26 3:41 PM, Peter Zijlstra wrote: > On Wed, Jun 03, 2026 at 03:25:21PM +0530, Shrikanth Hegde wrote: >> Venkat reported a panic on powerpc-next tree where GENERIC_ENTRY has >> been enabled. >> >> kernel BUG at kernel/sched/core.c:7512! >> NIP preempt_schedule_irq+0x44/0x118 >> LR dynamic_irqentry_exit_cond_resched+0x40/0x1a4 >> Call Trace: >> dynamic_irqentry_exit_cond_resched+0x40/0x1a4 >> do_page_fault+0xc0/0x104 >> data_access_common_virt+0x210/0x220 >> >> This happens since __do_page_fault ends up enabling the interrupts and >> it could take significant time such that need_resched could be set. This >> leads to schedule call in irqentry_exit leading to the bug. >> >> There are many such irq handlers which enables the interrupts. >> Fix it by disabling the irq before calling irqentry_exit. The same >> pattern exists today in interrupt_exit_kernel_prepare. >> >> While there, make those BUG_ON into WARN_ON. Interrupt is disabled right >> after so it is not that severe. This will still help to catch the >> offending callsites. >> >> Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature") >> Reported-by: Venkat Rao Bagalkote >> Closes: https://lore.kernel.org/all/7904105b-9dfa-4efd-a5ef-bc0276ed255d@linux.ibm.com/ >> Signed-off-by: Shrikanth Hegde >> --- >> >> This applies on top on powerpc/next tree. >> base: 6ed60999d33d '("powerpc: Remove unused functions")' >> >> arch/powerpc/include/asm/entry-common.h | 9 +++++---- >> 1 file changed, 5 insertions(+), 4 deletions(-) >> >> diff --git a/arch/powerpc/include/asm/entry-common.h b/arch/powerpc/include/asm/entry-common.h >> index de5601282755..7da373a56813 100644 >> --- a/arch/powerpc/include/asm/entry-common.h >> +++ b/arch/powerpc/include/asm/entry-common.h >> @@ -253,16 +253,17 @@ static inline void arch_interrupt_enter_prepare(struct pt_regs *regs) >> static inline void arch_interrupt_exit_prepare(struct pt_regs *regs) >> { >> if (user_mode(regs)) { >> - BUG_ON(regs_is_unrecoverable(regs)); >> - BUG_ON(regs_irqs_disabled(regs)); >> + WARN_ON(regs_is_unrecoverable(regs)); >> + WARN_ON(regs_irqs_disabled(regs)); > > So while you will indeed disable IRQs righ below. This checks the IRQ > state of regs, not the current state. > > What you are allowing through it a *userspace* state that has IRQs > disabled. That is an invalid state. Ok. I should have seen it closely. Let me keep them as is. > >> /* >> * We don't need to restore AMR on the way back to userspace for KUAP. >> * AMR can only have been unlocked if we interrupted the kernel. >> */ >> kuap_assert_locked(); >> - >> - local_irq_disable(); >> } >> + >> + /* irqentry_exit expects to be called with interrupts disabled */ >> + local_irq_disable(); >> } >> >> static inline void arch_interrupt_async_enter_prepare(struct pt_regs *regs) >> -- >> 2.47.3 >>