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Fri, 8 May 2026 04:12:58 +0000 (GMT) From: Aboorva Devarajan To: Madhavan Srinivasan , Athira Rajeev , linuxppc-dev@lists.ozlabs.org Cc: Aboorva Devarajan , Christophe Leroy , Kajol Jain , linux-kernel@vger.kernel.org Subject: [PATCH] powerpc/hv-gpci: fix preempt count leak in sysfs show paths Date: Fri, 8 May 2026 09:42:56 +0530 Message-ID: <20260508041256.3447113-1-aboorvad@linux.ibm.com> X-Mailer: git-send-email 2.54.0 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-Spam-Details-Enc: AW1haW4tMjYwNTA4MDAzNyBTYWx0ZWRfX3XztpEN77xxy wjQQVl3cPDyEsb/K+nn1DYMyjE1X+VhUJocpuyokCVVc11rMKx62tTZckBYxbGYEB82Tas13iOh E3Pen9YkqyWrrJ+fL+sorE6F91rhdXMNr7xt1HeIo9ZbdfVbAwE5EqI2F28Uk3+Bv/L3w9gXHnx 5PYeq9E/aTxIcfqgp5Akfp6UN07KRhJjxgR5M4qAVIUOqdF5nJ+7DhJHMlc+WwscGBNHbX5Vf2+ 3PStbIbtmBdCGu9ajLlLQGgkzBC0ntmvjN5K0pAv8s+KVJ/mME9xkhWiUezpyOWWh0SxU0Kuyne pziAv26Ni7WmRR+sdIW5XWFYo6gE4HAPulkJHhHojN79ZVrOWG/5cvXR2BMYEUYr9pYk7OXft3U leLCzeo7VwlPls14M6fILV1p6AoBqjRiO0r23uiFZ3RaDFh/wgduuXXXbbB2HUEex6udCRnSNWm bPbljYXcJOgHhA7xg9w== X-Proofpoint-ORIG-GUID: pJfAMLicPFT8ASpwj32WUG1nLKEl1xzr X-Proofpoint-GUID: pJfAMLicPFT8ASpwj32WUG1nLKEl1xzr X-Authority-Analysis: v=2.4 cv=ctWrVV4i c=1 sm=1 tr=0 ts=69fd62d2 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VnNF1IyMAAAA:8 a=T1Q85W7wrbM6iIICI_EA:9 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=2026-05-07_02,2026-05-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 lowpriorityscore=0 adultscore=0 clxscore=1011 suspectscore=0 impostorscore=0 spamscore=0 malwarescore=0 phishscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605080037 Four sysfs show() callbacks in hv-gpci take get_cpu_var(hv_gpci_reqb) (which calls preempt_disable()) but only call the matching put_cpu_var() on the error path under the 'out:' label. Every successful read leaks one preempt_disable(): processor_bus_topology_show() processor_config_show() affinity_domain_via_virtual_processor_show() affinity_domain_via_domain_show() (affinity_domain_via_partition_show() was already correct.) On a CONFIG_PREEMPT=y kernel, repeated reads raise preempt_count and eventually return to userspace with preemption still disabled. The next user-mode page fault then hits faulthandler_disabled() == 1, gets forced to SIGSEGV, and the resulting coredump trips 'BUG: scheduling while atomic' in call_usermodehelper_exec -> wait_for_completion_state -> schedule: BUG: scheduling while atomic: //0x00000004 ... __schedule_bug+0x6c/0x90 __schedule+0x58c/0x13a0 schedule+0x48/0x1a0 schedule_timeout+0x104/0x170 wait_for_completion_state+0x16c/0x330 call_usermodehelper_exec+0x254/0x2d0 vfs_coredump+0x1050/0x2590 get_signal+0xb9c/0xc80 do_notify_resume+0xf8/0x470 Add an out_success label that calls put_cpu_var() before returning the byte count, mirroring affinity_domain_via_partition_show(). Fixes: 71f1c39647d8 ("powerpc/hv_gpci: Add sysfs file inside hv_gpci device to show processor bus topology information") Fixes: 1a160c2a13c6 ("powerpc/hv_gpci: Add sysfs file inside hv_gpci device to show processor config information") Fixes: 71a7ccb478fc ("powerpc/hv_gpci: Add sysfs file inside hv_gpci device to show affinity domain via virtual processor information") Fixes: a69a57cac1ec ("powerpc/hv_gpci: Add sysfs file inside hv_gpci device to show affinity domain via domain information") Signed-off-by: Aboorva Devarajan --- arch/powerpc/perf/hv-gpci.c | 24 ++++++++++++++++-------- 1 file changed, 16 insertions(+), 8 deletions(-) diff --git a/arch/powerpc/perf/hv-gpci.c b/arch/powerpc/perf/hv-gpci.c index 5cac2cf3bd1e5..10c82cf8f5b39 100644 --- a/arch/powerpc/perf/hv-gpci.c +++ b/arch/powerpc/perf/hv-gpci.c @@ -210,7 +210,7 @@ static ssize_t processor_bus_topology_show(struct device *dev, struct device_att 0, 0, buf, &n, arg); if (!ret) - return n; + goto out_success; if (ret != H_PARAMETER) goto out; @@ -244,12 +244,14 @@ static ssize_t processor_bus_topology_show(struct device *dev, struct device_att starting_index, 0, buf, &n, arg); if (!ret) - return n; + goto out_success; if (ret != H_PARAMETER) goto out; } +out_success: + put_cpu_var(hv_gpci_reqb); return n; out: @@ -278,7 +280,7 @@ static ssize_t processor_config_show(struct device *dev, struct device_attribute 0, 0, buf, &n, arg); if (!ret) - return n; + goto out_success; if (ret != H_PARAMETER) goto out; @@ -312,12 +314,14 @@ static ssize_t processor_config_show(struct device *dev, struct device_attribute starting_index, 0, buf, &n, arg); if (!ret) - return n; + goto out_success; if (ret != H_PARAMETER) goto out; } +out_success: + put_cpu_var(hv_gpci_reqb); return n; out: @@ -346,7 +350,7 @@ static ssize_t affinity_domain_via_virtual_processor_show(struct device *dev, 0, 0, buf, &n, arg); if (!ret) - return n; + goto out_success; if (ret != H_PARAMETER) goto out; @@ -382,12 +386,14 @@ static ssize_t affinity_domain_via_virtual_processor_show(struct device *dev, starting_index, secondary_index, buf, &n, arg); if (!ret) - return n; + goto out_success; if (ret != H_PARAMETER) goto out; } +out_success: + put_cpu_var(hv_gpci_reqb); return n; out: @@ -416,7 +422,7 @@ static ssize_t affinity_domain_via_domain_show(struct device *dev, struct device 0, 0, buf, &n, arg); if (!ret) - return n; + goto out_success; if (ret != H_PARAMETER) goto out; @@ -448,12 +454,14 @@ static ssize_t affinity_domain_via_domain_show(struct device *dev, struct device starting_index, 0, buf, &n, arg); if (!ret) - return n; + goto out_success; if (ret != H_PARAMETER) goto out; } +out_success: + put_cpu_var(hv_gpci_reqb); return n; out: -- 2.54.0