From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta1.migadu.com (out-186.mta1.migadu.com [95.215.58.186]) (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 A60BD81724 for ; Thu, 6 Nov 2025 03:28:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762399734; cv=none; b=p1VQ9EBZRCtOfONLxag3ocL6zg/FnRQrFUCm1AEvpQ3CjVgXoWPcEpiChHUORZKq3bGZzM4Xt1Ifzj+2aLaD7Y0fvHKoZcqwoAewDjbgr2c3nLXxt3Y+7aljO7SiNHH4xES8g+jxmwF/8feeVF3gD+a2KNDjLGAZel3MDSayKiE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762399734; c=relaxed/simple; bh=0BQCa8hNbb+t+69Php3hIWt0TTjc1rlkRaAJl3nb2Kk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=f90b7Ptx6RvqV7lgGLiaKBIN6zEH+iKWAtAATz8wc2j2ZLrjs751T6KQXp2W1b/kBPkEDychhIN7OEDUvGQJ2/QjLHldeHbbhFpvUFOOdqi9rdLn8IX7g1jQ4hDbpkubDIf6UMNJ05C8xL+wFYKL+i/BgXpQdpNwMkQ2JCdcL58= 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=SeDLriDY; arc=none smtp.client-ip=95.215.58.186 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="SeDLriDY" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1762399729; 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=eInA+5LVUWWEAY2CBzLg/Er8itb5rM/VWoopvhS2+LQ=; b=SeDLriDYBEb/CHGZEqZsOfHJnj8Vxz/lEX+hHD3yRx6DzDp2eREpKcU93JHAlqUzg3RCEF m5nl4Dw5QwMx+dnT92L7206Imu9RB002G5W+H+EWohryEXJBgjn3r00gzerdDRuopV3tVy iW4kU7vTgoSYZX5KX93hePfleMb9bb8= Date: Thu, 6 Nov 2025 11:28:37 +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 To: Yonghong Song , 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: Tao Chen In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 在 2025/11/6 04:45, Yonghong Song 写道: > > > 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(). > Hi Yonghong, Thanks for your report, you are right. Maybe we should keep the get_perf_callchain parameters unchanged. I will change it in v5. > 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; >>   } > -- Best Regards Tao Chen