From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-189.mta0.migadu.com (out-189.mta0.migadu.com [91.218.175.189]) (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 B8B1F17993 for ; Wed, 5 Nov 2025 20:45:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762375539; cv=none; b=nBlS5yJzWeej1FPbAi+6kgqZ4QVGt699YagZwf2gWkRJDixHCVZxtRzoNBnyzgSOWrw/ljTrVEwI5cKAxJhZryv1nRC14HGqZzSB5/xTqxmhJFzXVrC0hYurNNJaiHa01eSGnuRn+58q/C61Mwbn7ynrN4ZbSdOVVSkoNj/uvwg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762375539; c=relaxed/simple; bh=usZuEfgTiQjSdoGWOEKccGdEdjv0wfrgaBT3Xw39F64=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=n0EnGkeFF1nFRUsfCZVdFvmlcOeXYt70Pokb2oVD+d6+yPafs2O4sq2CW9sSYgVnLEbj5wadj0O8aB2P4jZtdCiob0sLN88pIaRIZ2ik/uZDSdlq6bJfz/G/n+aIH1wsTt7YFR0rvqYNodkA42WT4kZuNUrvi/ViTIiwJAwsVi0= 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=jOWw9QaQ; arc=none smtp.client-ip=91.218.175.189 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="jOWw9QaQ" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1762375525; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=uYHtYxEt0GXZ3t+T7LTvPbBdGxB31zAaoF7FHEzvEl8=; b=jOWw9QaQmnq5H+hRmtWbA7Vh0xUKS3kjcTe5QtO3EKzUJ56iraZUg3nrHnfDUIzV+7Y/Dl 1sy5XiClQxWwcKjELrQJclqX/onQ8y4Pm4OkYP5mKlEtUYB+0M9wK9MUNJkTtYXzQRsLbL 4I+ZUAqpT5KU8hJYOaoAWdXd0YFdIIg= Date: Wed, 5 Nov 2025 12:45:15 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next v4 1/2] perf: Refactor get_perf_callchain Content-Language: en-GB To: Tao Chen , 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, 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 References: <20251028162502.3418817-1-chen.dylane@linux.dev> <20251028162502.3418817-2-chen.dylane@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: <20251028162502.3418817-2-chen.dylane@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 10/28/25 9:25 AM, Tao Chen wrote: > From BPF stack map, we want to use our own buffers to avoid > unnecessary copy and ensure that the buffer will not be > overwritten by other preemptive tasks. Peter suggested > provide more flexible stack-sampling APIs, which can be used > in BPF, and we can still use the perf callchain entry with > the help of these APIs. The next patch will modify the BPF part. > > Signed-off-by: Peter Zijlstra > Signed-off-by: Tao Chen > --- > include/linux/perf_event.h | 11 +++++- > kernel/bpf/stackmap.c | 4 +- > kernel/events/callchain.c | 75 ++++++++++++++++++++++++-------------- > kernel/events/core.c | 2 +- > 4 files changed, 61 insertions(+), 31 deletions(-) > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index fd1d91017b9..14a382cad1d 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -67,6 +67,7 @@ struct perf_callchain_entry_ctx { > u32 nr; > short contexts; > bool contexts_maxed; > + bool add_mark; > }; > > typedef unsigned long (*perf_copy_f)(void *dst, const void *src, > @@ -1718,9 +1719,17 @@ DECLARE_PER_CPU(struct perf_callchain_entry, perf_callchain_entry); > > extern void perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs); > extern void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs); > + > +extern void __init_perf_callchain_ctx(struct perf_callchain_entry_ctx *ctx, > + struct perf_callchain_entry *entry, > + u32 max_stack, bool add_mark); > + > +extern void __get_perf_callchain_kernel(struct perf_callchain_entry_ctx *ctx, struct pt_regs *regs); > +extern void __get_perf_callchain_user(struct perf_callchain_entry_ctx *ctx, struct pt_regs *regs); > + > extern struct perf_callchain_entry * > get_perf_callchain(struct pt_regs *regs, bool kernel, bool user, > - u32 max_stack, bool crosstask, bool add_mark); > + u32 max_stack, bool crosstask); > extern int get_callchain_buffers(int max_stack); > extern void put_callchain_buffers(void); > extern struct perf_callchain_entry *get_callchain_entry(int *rctx); > diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c > index 4d53cdd1374..e28b35c7e0b 100644 > --- a/kernel/bpf/stackmap.c > +++ b/kernel/bpf/stackmap.c > @@ -315,7 +315,7 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map, > max_depth = sysctl_perf_event_max_stack; > > trace = get_perf_callchain(regs, kernel, user, max_depth, > - false, false); > + false); This is not a refactor. Here, the add_mark parameter is removed. The 'add_mark' value here is expected to be false, but later get_perf_callchain(...) has 'add_mark' is true in __init_perf_callchain_ctx(). Applying this patch only on top of bpf-next master branch, we will have the following crash: [ 457.730077] bpf_testmod: oh no, recursing into test_1, recursion_misses 1 [ 460.221871] BUG: unable to handle page fault for address: fffa3bfffffff000 [ 460.221912] #PF: supervisor read access in kernel mode [ 460.221912] #PF: error_code(0x0000) - not-present page [ 460.221912] PGD 1e0ef1067 P4D 1e0ef0067 PUD 1e0eef067 PMD 1e0eee067 PTE 0 [ 460.221912] Oops: Oops: 0000 [#1] SMP KASAN NOPTI [ 460.221912] CPU: 2 UID: 0 PID: 2012 Comm: test_progs Tainted: G W OE 6.18.0-rc4-gafe2e8 [ 460.221912] Tainted: [W]=WARN, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE [ 460.221912] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-pr4 [ 460.221912] RIP: 0010:kasan_check_range+0x183/0x2c0 [ 460.221912] Code: 41 bf 08 00 00 00 41 29 ef 4d 01 fb 4d 29 de 4d 89 f4 4d 8d 6c 24 07 4d 85 e4 4d 0fd [ 460.221912] RSP: 0018:ff110001193bfc78 EFLAGS: 00010206 [ 460.221912] RAX: ffd1ffffffd5b301 RBX: dffffc0000000001 RCX: ffffffff819a2ecb [ 460.221912] RDX: 0000000000000001 RSI: 00000000ffffffb0 RDI: ffd1ffffffd5b360 [ 460.221912] RBP: 0000000000000004 R08: ffd20000ffd5b30f R09: 1ffa40001ffab661 [ 460.221912] R10: dffffc0000000000 R11: fffa3bfffffab670 R12: 000000001ffffff2 [ 460.221912] R13: 0000000003ff58cc R14: 0000000000053990 R15: 0000000000000000 [ 460.221912] FS: 00007f358c6460c0(0000) GS:ff110002384b4000(0000) knlGS:0000000000000000 [ 460.221912] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 460.221912] CR2: fffa3bfffffff000 CR3: 000000011468c006 CR4: 0000000000371ef0 [ 460.221912] Call Trace: [ 460.221912] [ 460.221912] __asan_memset+0x22/0x50 [ 460.221912] __bpf_get_stack+0x6eb/0x7a0 [ 460.221912] ? bpf_perf_event_output_raw_tp+0x58c/0x6c0 [ 460.221912] bpf_get_stack+0x1d/0x30 [ 460.221912] bpf_get_stack_raw_tp+0x148/0x180 [ 460.221912] bpf_prog_40e346a03dc2914c_bpf_prog1+0x169/0x1af [ 460.221912] bpf_trace_run2+0x1bc/0x350 [ 460.221912] ? bpf_trace_run2+0x104/0x350 [ 460.221912] ? trace_sys_enter+0x6b/0xf0 [ 460.221912] __bpf_trace_sys_enter+0x38/0x60 [ 460.221912] trace_sys_enter+0xa7/0xf0 [ 460.221912] syscall_trace_enter+0xfc/0x160 [ 460.221912] ? entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 460.221912] do_syscall_64+0x5a/0xfa0 [ 460.221912] ? asm_sysvec_apic_timer_interrupt+0x1a/0x20 [ 460.221912] entry_SYSCALL_64_after_hwframe+0x76/0x7e > > if (unlikely(!trace)) > /* couldn't fetch the stack trace */ > @@ -452,7 +452,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task, > trace = get_callchain_entry_for_task(task, max_depth); > else > trace = get_perf_callchain(regs, kernel, user, max_depth, > - crosstask, false); > + crosstask); > > if (unlikely(!trace) || trace->nr < skip) { > if (may_fault) > diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c > index 808c0d7a31f..2c36e490625 100644 > --- a/kernel/events/callchain.c > +++ b/kernel/events/callchain.c > @@ -216,13 +216,54 @@ static void fixup_uretprobe_trampoline_entries(struct perf_callchain_entry *entr > #endif > } > > +void __init_perf_callchain_ctx(struct perf_callchain_entry_ctx *ctx, > + struct perf_callchain_entry *entry, > + u32 max_stack, bool add_mark) > + > +{ > + ctx->entry = entry; > + ctx->max_stack = max_stack; > + ctx->nr = entry->nr = 0; > + ctx->contexts = 0; > + ctx->contexts_maxed = false; > + ctx->add_mark = add_mark; > +} > + > +void __get_perf_callchain_kernel(struct perf_callchain_entry_ctx *ctx, struct pt_regs *regs) > +{ > + if (user_mode(regs)) > + return; > + > + if (ctx->add_mark) > + perf_callchain_store_context(ctx, PERF_CONTEXT_KERNEL); > + perf_callchain_kernel(ctx, regs); > +} > + > +void __get_perf_callchain_user(struct perf_callchain_entry_ctx *ctx, struct pt_regs *regs) > +{ > + int start_entry_idx; > + > + if (!user_mode(regs)) { > + if (current->flags & (PF_KTHREAD | PF_USER_WORKER)) > + return; > + regs = task_pt_regs(current); > + } > + > + if (ctx->add_mark) > + perf_callchain_store_context(ctx, PERF_CONTEXT_USER); > + > + start_entry_idx = ctx->nr; > + perf_callchain_user(ctx, regs); > + fixup_uretprobe_trampoline_entries(ctx->entry, start_entry_idx); > +} > + > struct perf_callchain_entry * > get_perf_callchain(struct pt_regs *regs, bool kernel, bool user, > - u32 max_stack, bool crosstask, bool add_mark) > + u32 max_stack, bool crosstask) > { > struct perf_callchain_entry *entry; > struct perf_callchain_entry_ctx ctx; > - int rctx, start_entry_idx; > + int rctx; > > /* crosstask is not supported for user stacks */ > if (crosstask && user && !kernel) > @@ -232,34 +273,14 @@ get_perf_callchain(struct pt_regs *regs, bool kernel, bool user, > if (!entry) > return NULL; > > - ctx.entry = entry; > - ctx.max_stack = max_stack; > - ctx.nr = entry->nr = 0; > - ctx.contexts = 0; > - ctx.contexts_maxed = false; > + __init_perf_callchain_ctx(&ctx, entry, max_stack, true); > > - if (kernel && !user_mode(regs)) { > - if (add_mark) > - perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL); > - perf_callchain_kernel(&ctx, regs); > - } > - > - if (user && !crosstask) { > - if (!user_mode(regs)) { > - if (current->flags & (PF_KTHREAD | PF_USER_WORKER)) > - goto exit_put; > - regs = task_pt_regs(current); > - } > + if (kernel) > + __get_perf_callchain_kernel(&ctx, regs); > > - if (add_mark) > - perf_callchain_store_context(&ctx, PERF_CONTEXT_USER); > - > - start_entry_idx = entry->nr; > - perf_callchain_user(&ctx, regs); > - fixup_uretprobe_trampoline_entries(entry, start_entry_idx); > - } > + if (user && !crosstask) > + __get_perf_callchain_user(&ctx, regs); > > -exit_put: > put_callchain_entry(rctx); > > return entry; > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 7541f6f85fc..eb0f110593d 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -8218,7 +8218,7 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs) > return &__empty_callchain; > > callchain = get_perf_callchain(regs, kernel, user, > - max_stack, crosstask, true); > + max_stack, crosstask); > return callchain ?: &__empty_callchain; > } >