From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-187.mta1.migadu.com (out-187.mta1.migadu.com [95.215.58.187]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 279161F1932 for ; Sun, 19 Oct 2025 17:02:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.187 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760893378; cv=none; b=MNt8aQIUJcySKHCyrtlgLpWBJgTx38iWXvKCsFyQsTnPzJ7yWRicsL34bcJz3pAl9QdUnKlCDISZabaC604mZ5Ax0I6qA3o7JtU9BWLByi/iyl5R+G91cCoAEbVVRa1hSZ7lkl7apZgAfQYSEmqAv0y6Xbdyo+MA5iusKtNErIw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760893378; c=relaxed/simple; bh=IyZjViwTU+fSQl3iL4ueU5R8mVHc97l1RDbxLFnrsxg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RFw7lXQYIGBYVQf0Wj/zD5ASfTPzi43WEs6sBz3C1bbFXf9Y3wbh1SIw79fDDatUIhAvdxjRXjSSBWDKLOLqzn+STm6XiwJUhCfj+vXybhq2Tf14hNAwOeC2L/im+h8aiwnAe7DMtuXtA5EIkzdVJgPLBavDsKrDeXKAo5dDtK0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=KrdcmypE; arc=none smtp.client-ip=95.215.58.187 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="KrdcmypE" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1760893373; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=pxR+wVdAhjEEI7Bc6zUqxvsQr4183O0pz8aYIFFkFmg=; b=KrdcmypERZIFuzr/c7iiyFAvZRnaoNVgXQd29zvujjnoCKexbhkWiAkfCKbdI/KL3lEcbW iSfwtY+IeBv6wM8J8HLdtUOkseWeoxWCJ4R5VoAgSGzW0dEFmAR/zXvgpb3GVcVVw9tFkB bHWvlirnGRVpHBIgwosJdbjrA7wnuBY= From: Tao Chen To: peterz@infradead.org, mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com, song@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com Cc: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Tao Chen Subject: [PATCH bpf-next v3 2/2] bpf: Use per-cpu BPF callchain entry to save callchain Date: Mon, 20 Oct 2025 01:01:18 +0800 Message-ID: <20251019170118.2955346-3-chen.dylane@linux.dev> In-Reply-To: <20251019170118.2955346-1-chen.dylane@linux.dev> References: <20251019170118.2955346-1-chen.dylane@linux.dev> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT As Alexei noted, get_perf_callchain() return values may be reused if a task is preempted after the BPF program enters migrate disable mode. Drawing on the per-cpu design of bpf_bprintf_buffers, per-cpu BPF callchain entry is used here. Signed-off-by: Tao Chen --- kernel/bpf/stackmap.c | 98 ++++++++++++++++++++++++++++++++----------- 1 file changed, 74 insertions(+), 24 deletions(-) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 94e46b7f340..3513077c57d 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -31,6 +31,52 @@ struct bpf_stack_map { struct stack_map_bucket *buckets[] __counted_by(n_buckets); }; +struct bpf_perf_callchain_entry { + u64 nr; + u64 ip[PERF_MAX_STACK_DEPTH]; +}; + +#define MAX_PERF_CALLCHAIN_PREEMPT 3 +static DEFINE_PER_CPU(struct bpf_perf_callchain_entry[MAX_PERF_CALLCHAIN_PREEMPT], + bpf_perf_callchain_entries); +static DEFINE_PER_CPU(int, bpf_perf_callchain_preempt_cnt); + +static int bpf_get_perf_callchain_or_entry(struct perf_callchain_entry **entry, + struct pt_regs *regs, bool kernel, + bool user, u32 max_stack, bool crosstack, + bool add_mark, bool get_callchain) +{ + struct bpf_perf_callchain_entry *bpf_entry; + struct perf_callchain_entry *perf_entry; + int preempt_cnt; + + preempt_cnt = this_cpu_inc_return(bpf_perf_callchain_preempt_cnt); + if (WARN_ON_ONCE(preempt_cnt > MAX_PERF_CALLCHAIN_PREEMPT)) { + this_cpu_dec(bpf_perf_callchain_preempt_cnt); + return -EBUSY; + } + + bpf_entry = this_cpu_ptr(&bpf_perf_callchain_entries[preempt_cnt - 1]); + if (!get_callchain) { + *entry = (struct perf_callchain_entry *)bpf_entry; + return 0; + } + + perf_entry = get_perf_callchain(regs, (struct perf_callchain_entry *)bpf_entry, + kernel, user, max_stack, + crosstack, add_mark); + *entry = perf_entry; + + return 0; +} + +static void bpf_put_perf_callchain(void) +{ + if (WARN_ON_ONCE(this_cpu_read(bpf_perf_callchain_preempt_cnt) == 0)) + return; + this_cpu_dec(bpf_perf_callchain_preempt_cnt); +} + static inline bool stack_map_use_build_id(struct bpf_map *map) { return (map->map_flags & BPF_F_STACK_BUILD_ID); @@ -192,11 +238,11 @@ get_callchain_entry_for_task(struct task_struct *task, u32 max_depth) { #ifdef CONFIG_STACKTRACE struct perf_callchain_entry *entry; - int rctx; - - entry = get_callchain_entry(&rctx); + int ret; - if (!entry) + ret = bpf_get_perf_callchain_or_entry(&entry, NULL, false, false, 0, false, false, + false); + if (ret) return NULL; entry->nr = stack_trace_save_tsk(task, (unsigned long *)entry->ip, @@ -216,7 +262,7 @@ get_callchain_entry_for_task(struct task_struct *task, u32 max_depth) to[i] = (u64)(from[i]); } - put_callchain_entry(rctx); + bpf_put_perf_callchain(); return entry; #else /* CONFIG_STACKTRACE */ @@ -305,6 +351,7 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map, bool user = flags & BPF_F_USER_STACK; struct perf_callchain_entry *trace; bool kernel = !user; + int err; if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK | BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID))) @@ -314,14 +361,15 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map, if (max_depth > sysctl_perf_event_max_stack) max_depth = sysctl_perf_event_max_stack; - trace = get_perf_callchain(regs, NULL, kernel, user, max_depth, - false, false); + err = bpf_get_perf_callchain_or_entry(&trace, regs, kernel, user, max_depth, + false, false, true); + if (err) + return err; - if (unlikely(!trace)) - /* couldn't fetch the stack trace */ - return -EFAULT; + err = __bpf_get_stackid(map, trace, flags); + bpf_put_perf_callchain(); - return __bpf_get_stackid(map, trace, flags); + return err; } const struct bpf_func_proto bpf_get_stackid_proto = { @@ -443,20 +491,23 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task, if (sysctl_perf_event_max_stack < max_depth) max_depth = sysctl_perf_event_max_stack; - if (may_fault) - rcu_read_lock(); /* need RCU for perf's callchain below */ - if (trace_in) trace = trace_in; - else if (kernel && task) + else if (kernel && task) { trace = get_callchain_entry_for_task(task, max_depth); - else - trace = get_perf_callchain(regs, NULL, kernel, user, max_depth, - crosstask, false); + } else { + err = bpf_get_perf_callchain_or_entry(&trace, regs, kernel, user, max_depth, + false, false, true); + if (err) + return err; + } + + if (unlikely(!trace)) + goto err_fault; - if (unlikely(!trace) || trace->nr < skip) { - if (may_fault) - rcu_read_unlock(); + if (trace->nr < skip) { + if (!trace_in) + bpf_put_perf_callchain(); goto err_fault; } @@ -475,9 +526,8 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task, memcpy(buf, ips, copy_len); } - /* trace/ips should not be dereferenced after this point */ - if (may_fault) - rcu_read_unlock(); + if (!trace_in) + bpf_put_perf_callchain(); if (user_build_id) stack_map_get_build_id_offset(buf, trace_nr, user, may_fault); -- 2.48.1