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Wed, 3 Jun 2026 06:28:01 +0000 (GMT) From: Aboorva Devarajan To: Madhavan Srinivasan , linuxppc-dev@lists.ozlabs.org Cc: Athira Rajeev , Aboorva Devarajan , Christophe Leroy , linux-kernel@vger.kernel.org, Sourabh Jain , Ritesh Harjani , Shrikanth Hegde Subject: [PATCH 3/3] powerpc/kexec: fix double get_cpu() imbalance in kexec_prepare_cpus Date: Wed, 3 Jun 2026 11:57:43 +0530 Message-ID: <20260603062743.1152253-4-aboorvad@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260603062743.1152253-1-aboorvad@linux.ibm.com> References: <20260603062743.1152253-1-aboorvad@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: yUIY4cDnkKZJp1H322_jgn677HP3tL2k X-Proofpoint-GUID: u7iXvpUrp6lWhCOYoS685Vm5LWcDY0du X-Authority-Analysis: v=2.4 cv=bcVbluPB c=1 sm=1 tr=0 ts=6a1fc97a cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=VnNF1IyMAAAA:8 a=NZuQ31_9CfGeVvh8xa4A:9 a=O8hF6Hzn-FEA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjAzMDA1NiBTYWx0ZWRfXysn2RhiqjE8Y TzpEo4UPiNtYXhYBF2pXXLCho1VY2q5T8wKSi+iazq5fq1fQq3rmoPtIMZgiWV9ltGd7UPhe/wi YXqxSvk0s41cfCDGTdU3aW8xV38oQ6bGR+GyDPwQ3zvaOOPRF6nxChXH/awc3rlryGu+nKArY0S 5eqFYaurM/LNmJ24HGrcYS5N3zIaNkSAkS03eHdYDNFA4rocy/LgPwR31gwQwEeYLRISusc157V gl2pEg1YvWJfJB8ELREl9uTQYS6VigK0wv3iE9WDj7YTccT9MCkZ/8stybQsAq9Y6klLedzxGfv H9w6ZlqCkajilGLFT4yMCYbRuq8ZPV0+vH418p7oSLWMWHwa5jfR+q/Pw8bSJxobJf20urKWTk9 TiKAqNVGz7g6lQzmDNP5XADIrjj4eDj5LTr8AhOWDuv2puIPZqqkiJDC1ViZ3M7gyAZSzXoQU05 Jx7zER+aHgwy6s28aBA== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-06-03_02,2026-05-28_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 clxscore=1015 adultscore=0 priorityscore=1501 phishscore=0 lowpriorityscore=0 bulkscore=0 malwarescore=0 spamscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605210000 definitions=main-2606030056 kexec_prepare_cpus_wait() calls get_cpu() internally to obtain the current CPU id. kexec_prepare_cpus() calls kexec_prepare_cpus_wait() twice -- once for KEXEC_STATE_IRQS_OFF and once for KEXEC_STATE_REAL_MODE -- but only issues a single put_cpu() at the end, leaving preempt_count elevated by one extra nesting level. In practice the imbalance does not trigger a 'scheduling while atomic' splat because the kexec path is a one-way trip: IRQs are already disabled, no schedule() occurs after the leak, and default_machine_kexec() overwrites preempt_count with HARDIRQ_OFFSET before jumping into kexec_sequence() which never returns. However the bookkeeping is still wrong. kexec_prepare_cpus() calls local_irq_disable()/hard_irq_disable() before invoking kexec_prepare_cpus_wait(), so the CPU is already pinned and the get_cpu()/put_cpu() preempt_disable() bracketing is unnecessary. Only the current CPU id is needed, so replace get_cpu() with smp_processor_id() and drop the now-unneeded put_cpu(). Fixes: 1fc711f7ffb0 ("powerpc/kexec: Fix race in kexec shutdown") Signed-off-by: Aboorva Devarajan --- arch/powerpc/kexec/core_64.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/arch/powerpc/kexec/core_64.c b/arch/powerpc/kexec/core_64.c index 825ab8a88f18..d7bdc362d497 100644 --- a/arch/powerpc/kexec/core_64.c +++ b/arch/powerpc/kexec/core_64.c @@ -169,7 +169,7 @@ static void kexec_prepare_cpus_wait(int wait_state) int my_cpu, i, notified=-1; hw_breakpoint_disable(); - my_cpu = get_cpu(); + my_cpu = smp_processor_id(); /* Make sure each CPU has at least made it to the state we need. * * FIXME: There is a (slim) chance of a problem if not all of the CPUs @@ -267,8 +267,6 @@ static void kexec_prepare_cpus(void) /* after we tell the others to go down */ if (ppc_md.kexec_cpu_down) ppc_md.kexec_cpu_down(0, 0); - - put_cpu(); } #else /* ! SMP */ -- 2.54.0