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Tue, 29 Aug 2023 06:35:16 +0000 (GMT) Received: from ozlabs.au.ibm.com (unknown [9.192.253.14]) by smtpav05.fra02v.mail.ibm.com (Postfix) with ESMTP for ; Tue, 29 Aug 2023 06:35:16 +0000 (GMT) Received: from bgray-lenovo-p15.ozlabs.ibm.com (haven.au.ibm.com [9.192.254.114]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.au.ibm.com (Postfix) with ESMTPSA id 8419960595; Tue, 29 Aug 2023 16:35:13 +1000 (AEST) From: Benjamin Gray To: linuxppc-dev@lists.ozlabs.org Subject: [PATCH 1/3] powerpc/watchpoints: Disable preemption in thread_change_pc() Date: Tue, 29 Aug 2023 16:34:55 +1000 Message-ID: <20230829063457.54157-2-bgray@linux.ibm.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230829063457.54157-1-bgray@linux.ibm.com> References: <20230829063457.54157-1-bgray@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: QjMYcHKWHCZ5MGH2vQhgVRn3L4mVzkD0 X-Proofpoint-GUID: QjMYcHKWHCZ5MGH2vQhgVRn3L4mVzkD0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.957,Hydra:6.0.601,FMLib:17.11.176.26 definitions=2023-08-29_03,2023-08-28_04,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 mlxscore=0 adultscore=0 impostorscore=0 mlxlogscore=999 malwarescore=0 bulkscore=0 clxscore=1015 priorityscore=1501 spamscore=0 phishscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2308100000 definitions=main-2308290056 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Benjamin Gray Errors-To: linuxppc-dev-bounces+incoming=patchwork.ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" thread_change_pc() uses CPU local data, so must be protected from swapping CPUs while it is reading the breakpoint struct. The error is more noticeable after 1e60f3564bad ("powerpc/watchpoints: Track perf single step directly on the breakpoint"), which added an unconditional __this_cpu_read() call in thread_change_pc(). However the existing __this_cpu_read() that runs if a breakpoint does need to be re-inserted has the same issue. Signed-off-by: Benjamin Gray --- There's probably a more idiomatic way to express this. We technically don't need to disable preemption for the entire function: we should only need to disable preemption within each loop iteration while handling the pointer we are working with. Each iteration itself is independent. --- arch/powerpc/kernel/hw_breakpoint.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c index b8513dc3e53a..2854376870cf 100644 --- a/arch/powerpc/kernel/hw_breakpoint.c +++ b/arch/powerpc/kernel/hw_breakpoint.c @@ -230,13 +230,15 @@ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs) struct arch_hw_breakpoint *info; int i; + preempt_disable(); + for (i = 0; i < nr_wp_slots(); i++) { struct perf_event *bp = __this_cpu_read(bp_per_reg[i]); if (unlikely(bp && counter_arch_bp(bp)->perf_single_step)) goto reset; } - return; + goto out; reset: regs_set_return_msr(regs, regs->msr & ~MSR_SE); @@ -245,6 +247,9 @@ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs) __set_breakpoint(i, info); info->perf_single_step = false; } + +out: + preempt_enable(); } static bool is_larx_stcx_instr(int type)