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Fri, 5 Jun 2026 08:29:21 +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 v3 1/3] powerpc/perf: fix preempt count underflow in fsl_emb_pmu_del Date: Fri, 5 Jun 2026 13:59:10 +0530 Message-ID: <20260605082912.305100-2-aboorvad@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260605082912.305100-1-aboorvad@linux.ibm.com> References: <20260605082912.305100-1-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: QhuRXniilY9g37LaWRLncqNVFvaFfz-S X-Proofpoint-GUID: Cxst93E8hevUwdl3z3Z0r8g8nkqmtq-p X-Authority-Analysis: v=2.4 cv=bcVbluPB c=1 sm=1 tr=0 ts=6a2288e9 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=VnNF1IyMAAAA:8 a=-qzNKB2iBSQ2TZesQmUA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjA1MDA3NyBTYWx0ZWRfX8T3xz0xqONHA Y+D3/ur3bcWcXvoINChZj5Jgec1gfiG4bOqR+gsO/sxqOcwgylh1PRNqMmrTxJWs4SUaej0MXIS 0VLUMmOVyOSCRP9R65n1oYl4UHr2GaVWFzSUpcDz/Cp0QbAfkTEYGADbx/VidgQWyQio5lG778f /2qVCedsNMZ3eDNZzOTyq3JsbJxm4pbBImvHVDylBVhpd6Zu3U/ijLuMjk/PelKE6fdwFEzYCOG TkIaKPNoFUfInHGm2d5esimObcgd37Hvrj5GlKlYC9YWYTE2WzAE7kuiNSgzCr2HPmBuEGv37A7 Bvq32WH911K5rTbPKXKOIxO8H+LHuyzbiaZxLty0SxUI8C0q2p9KuRVh7qTwgLFJyhUkkRaE21g 5gQB2yzdI66uU1i/pPzAfHw1MKECuCT4HBpBX+VcbZb/t308tjzfEu7mSLvLrD6sFzQ3a07WRRK /hkKC0IhSD+50LIT4lA== 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=2026-06-05_01,2026-05-28_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-2606050077 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: a11106544f33 ("powerpc/perf: e500 support") Reviewed-by: Shrikanth Hegde 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 7120ab20cbfe..02b5dd74c187 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) -- 2.54.0