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Mon, 18 May 2026 06:13:11 +0000 (GMT) Received: from [9.123.5.233] (unknown [9.123.5.233]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 18 May 2026 06:13:11 +0000 (GMT) Message-ID: <1e31821a-2c9d-4394-83b4-e850f96ad662@linux.ibm.com> Date: Mon, 18 May 2026 11:43:11 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] powerpc/perf: fix preempt count underflow in fsl_emb_pmu_del To: Aboorva Devarajan , Madhavan Srinivasan , linuxppc-dev@lists.ozlabs.org Cc: Athira Rajeev , Christophe Leroy , linux-kernel@vger.kernel.org, Sourabh Jain , Ritesh Harjani References: <20260518050855.1147242-1-aboorvad@linux.ibm.com> <20260518050855.1147242-2-aboorvad@linux.ibm.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <20260518050855.1147242-2-aboorvad@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: 3QaU4Ms63bUdZFAAcWmKBPOLkASZAsP6 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTE4MDA1NiBTYWx0ZWRfX6UXTAr2kM5eY SsIxqMHbAEjJGEkZlPad0lgcgWlal9/tdeM4N6lMhUhm2EkxwF2ObQc9MdxjdoT/dOfpCvrdMSI uNt2EkfiAOF8kNatAtg5eKaaq0MDbPV6lsBXB2iG2f+R6pwAvVrNn2N3ZHb4bBQ3o4nvAU9h4MZ jtFYqs2qhxNqKt0rz2CP1NFRYuhkC69z0eO63xvk/5cOB1yCVUXGiFaR0EUdKeUg89HZHM2t9XS jKtUGPhtFSC0eLllBSltv3cCYq3U0SiBnBtkl9wJPDqLoJSvFsWr3nkLZoYgQBg8+3NGEW6MnHX 4lN9cQolYz9AN1Vcuexm0NVXqAi4CZ+54Usf3nVhF1CFv/6ImqFYx68U3GhKQA++1vCn2327B4w Fqm6u7yFLDp53cav9x4INbKOF5Ijg5xdmFb7mOtRRPNNtVmHKaEgTaWu5dFMjV13YBm+9KWP3Zg /fnjz3YkNAt1j46qRXA== X-Proofpoint-GUID: Oq97JMNFrYmqM5DbywPoBHAylMV4lsqQ X-Authority-Analysis: v=2.4 cv=apyCzyZV c=1 sm=1 tr=0 ts=6a0aadfe cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VnNF1IyMAAAA:8 a=BzsuWJ9IV0snJKnQtnoA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-18_01,2026-05-15_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 lowpriorityscore=0 priorityscore=1501 impostorscore=0 bulkscore=0 suspectscore=0 adultscore=0 spamscore=0 phishscore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605130000 definitions=main-2605180056 On 5/18/26 10:38 AM, Aboorva Devarajan wrote: > fsl_emb_pmu_del() unconditionally calls put_cpu_var(cpu_hw_events) at > the 'out:' label, but only calls the matching get_cpu_var() after the > 'i < 0' early-return check. When event->hw.idx is negative the > function jumps to 'out:' without having taken get_cpu_var(), and the > trailing put_cpu_var() then issues an unmatched preempt_enable(), > underflowing preempt_count. > > On a CONFIG_PREEMPT=y kernel preempt_count would underflow and > eventually present as a 'scheduling while atomic' BUG. > > Move put_cpu_var() to pair with get_cpu_var() so the percpu access is > correctly bracketed and the 'out:' label only handles perf_pmu_enable. > > Fixes: a11106544f33c ("powerpc/perf: e500 support") > Signed-off-by: Aboorva Devarajan > --- > arch/powerpc/perf/core-fsl-emb.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/perf/core-fsl-emb.c b/arch/powerpc/perf/core-fsl-emb.c > index 7120ab20cbfec..02b5dd74c187a 100644 > --- a/arch/powerpc/perf/core-fsl-emb.c > +++ b/arch/powerpc/perf/core-fsl-emb.c > @@ -366,9 +366,10 @@ static void fsl_emb_pmu_del(struct perf_event *event, int flags) > > cpuhw->n_events--; > > + put_cpu_var(cpu_hw_events); > + > out: > perf_pmu_enable(event->pmu); > - put_cpu_var(cpu_hw_events); > } > > static void fsl_emb_pmu_start(struct perf_event *event, int ef_flags) Thanks for fixing this. Looks good to me. Reviewed-by: Shrikanth Hegde