From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta1.migadu.com (out-173.mta1.migadu.com [95.215.58.173]) (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 7CCC0327C05 for ; Fri, 16 Jan 2026 04:35:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768538134; cv=none; b=hhEXNIUcuhHlQHNKm/ZlHPdTK1VbjJhKj8xgg+6CywR9W8jcTpI9W3s2c5frFw1X8Na9L6unxgjhzHvJPKWw7Pvq0PFxhmWAVqlGOu4x2Mam6nESWLB4me6ZBKqT8eTEPg/6oJgQJmYgCg8Zj84qSesFo0fjc9Up0qb3EPCVm2s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768538134; c=relaxed/simple; bh=J/Rpx69WQVWJmBctzDnKoQEU5I697W1VYyNDjIvQ2CI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ELUp5kkNqsNKtj0m9dxSC0shDW8ovZawW8Am83f19VGikIjZkOF7xTO0Vlo50uQPNWGAC4P+18AR8RX3D65GK7cq1E8zWN2F1eTFRIIXM2LdOeaUie4XPiw/5YqPvAVumwcNUmnnIfEjRkhEAWCd/0S7roAeWSFjQyu53ulN4hU= 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=F7nDuSyR; arc=none smtp.client-ip=95.215.58.173 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="F7nDuSyR" Message-ID: <6dbaff1f-09d3-421a-9813-c9c1cda8e7d8@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1768538129; 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=tI5hey17l5h284K+S50zyAtjfyhLgi4YnoQ9GpEBMZ8=; b=F7nDuSyROyEAdZI5M7UCLKzwk7eCpV63OZbD7paufIC1iRZA0hQ7EH6nVAeLFAyt3tJXlg G3iM/jz4E82gTjq3RWF4KpNpr7kBQzbkKYY0hHHikV8spjSeTzgvWFRdu67VD3WXnU2Dw3 jQOzH8uci/ATBh2EyNaWeQPuByYyXxY= Date: Fri, 16 Jan 2026 12:35:14 +0800 Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next v7 2/2] bpf: Hold the perf callchain entry until used completely To: Andrii Nakryiko , peterz@infradead.org Cc: 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, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org References: <20251217093326.1745307-1-chen.dylane@linux.dev> <20251217093326.1745307-3-chen.dylane@linux.dev> <0e954e9a-12af-4f4f-95e2-7afedbd8f63f@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 2026/1/10 07:47, Andrii Nakryiko 写道: > On Tue, Jan 6, 2026 at 8:00 AM Tao Chen wrote: >> >> 在 2025/12/23 14:29, Tao Chen 写道: >>> 在 2025/12/17 17:33, Tao Chen 写道: >>>> As Alexei noted, get_perf_callchain() return values may be reused >>>> if a task is preempted after the BPF program enters migrate disable >>>> mode. The perf_callchain_entres has a small stack of entries, and >>>> we can reuse it as follows: >>>> >>>> 1. get the perf callchain entry >>>> 2. BPF use... >>>> 3. put the perf callchain entry >>>> >>>> And Peter suggested that get_recursion_context used with preemption >>>> disabled, so we should disable preemption at BPF side. >>>> >>>> Acked-by: Yonghong Song >>>> Signed-off-by: Tao Chen >>>> --- >>>> kernel/bpf/stackmap.c | 68 +++++++++++++++++++++++++++++++++++-------- >>>> 1 file changed, 56 insertions(+), 12 deletions(-) >>>> >>>> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c >>>> index da3d328f5c1..3bdd99a630d 100644 >>>> --- a/kernel/bpf/stackmap.c >>>> +++ b/kernel/bpf/stackmap.c >>>> @@ -210,13 +210,14 @@ static void stack_map_get_build_id_offset(struct >>>> bpf_stack_build_id *id_offs, >>>> } >>>> static struct perf_callchain_entry * >>>> -get_callchain_entry_for_task(struct task_struct *task, u32 max_depth) >>>> +get_callchain_entry_for_task(int *rctx, struct task_struct *task, u32 >>>> max_depth) >>>> { >>>> #ifdef CONFIG_STACKTRACE >>>> struct perf_callchain_entry *entry; >>>> - int rctx; >>>> - entry = get_callchain_entry(&rctx); >>>> + preempt_disable(); >>>> + entry = get_callchain_entry(rctx); >>>> + preempt_enable(); >>>> if (!entry) >>>> return NULL; >>>> @@ -238,8 +239,6 @@ get_callchain_entry_for_task(struct task_struct >>>> *task, u32 max_depth) >>>> to[i] = (u64)(from[i]); >>>> } >>>> - put_callchain_entry(rctx); >>>> - >>>> return entry; >>>> #else /* CONFIG_STACKTRACE */ >>>> return NULL; >>>> @@ -320,6 +319,34 @@ static long __bpf_get_stackid(struct bpf_map *map, >>>> return id; >>>> } >>>> +static struct perf_callchain_entry * >>>> +bpf_get_perf_callchain(int *rctx, struct pt_regs *regs, bool kernel, >>>> bool user, >>>> + int max_stack, bool crosstask) >>>> +{ >>>> + struct perf_callchain_entry_ctx ctx; >>>> + struct perf_callchain_entry *entry; >>>> + >>>> + preempt_disable(); >>>> + entry = get_callchain_entry(rctx); >>>> + preempt_enable(); >>>> + >>>> + if (unlikely(!entry)) >>>> + return NULL; >>>> + >>>> + __init_perf_callchain_ctx(&ctx, entry, max_stack, false); >>>> + if (kernel) >>>> + __get_perf_callchain_kernel(&ctx, regs); >>>> + if (user && !crosstask) >>>> + __get_perf_callchain_user(&ctx, regs, 0); >>>> + >>>> + return entry; >>>> +} >>>> + >>>> +static void bpf_put_perf_callchain(int rctx) >>>> +{ >>>> + put_callchain_entry(rctx); >>>> +} >>>> + >>>> BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map >>>> *, map, >>>> u64, flags) >>>> { >>>> @@ -328,20 +355,25 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, >>>> regs, struct bpf_map *, map, >>>> struct perf_callchain_entry *trace; >>>> bool kernel = !user; >>>> u32 max_depth; >>>> + int rctx, ret; >>>> if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK | >>>> BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID))) >>>> return -EINVAL; >>>> max_depth = stack_map_calculate_max_depth(map->value_size, >>>> elem_size, flags); >>>> - trace = get_perf_callchain(regs, kernel, user, max_depth, >>>> - false, false, 0); >>>> + >>>> + trace = bpf_get_perf_callchain(&rctx, regs, kernel, user, max_depth, >>>> + false); >>>> if (unlikely(!trace)) >>>> /* couldn't fetch the stack trace */ >>>> return -EFAULT; >>>> - return __bpf_get_stackid(map, trace, flags); >>>> + ret = __bpf_get_stackid(map, trace, flags); >>>> + bpf_put_perf_callchain(rctx); >>>> + >>>> + return ret; >>>> } >>>> const struct bpf_func_proto bpf_get_stackid_proto = { >>>> @@ -435,6 +467,7 @@ static long __bpf_get_stack(struct pt_regs *regs, >>>> struct task_struct *task, >>>> bool kernel = !user; >>>> int err = -EINVAL; >>>> u64 *ips; >>>> + int rctx; >>>> if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK | >>>> BPF_F_USER_BUILD_ID))) >>>> @@ -467,18 +500,26 @@ static long __bpf_get_stack(struct pt_regs >>>> *regs, struct task_struct *task, >>>> trace = trace_in; >>>> trace->nr = min_t(u32, trace->nr, max_depth); >>>> } else if (kernel && task) { >>>> - trace = get_callchain_entry_for_task(task, max_depth); >>>> + trace = get_callchain_entry_for_task(&rctx, task, max_depth); >>>> } else { >>>> - trace = get_perf_callchain(regs, kernel, user, max_depth, >>>> - crosstask, false, 0); >>>> + trace = bpf_get_perf_callchain(&rctx, regs, kernel, user, >>>> max_depth, >>>> + crosstask); >>>> } >>>> - if (unlikely(!trace) || trace->nr < skip) { >>>> + if (unlikely(!trace)) { >>>> if (may_fault) >>>> rcu_read_unlock(); >>>> goto err_fault; >>>> } >>>> + if (trace->nr < skip) { >>>> + if (may_fault) >>>> + rcu_read_unlock(); >>>> + if (!trace_in) >>>> + bpf_put_perf_callchain(rctx); >>>> + goto err_fault; >>>> + } >>>> + >>>> trace_nr = trace->nr - skip; >>>> copy_len = trace_nr * elem_size; >>>> @@ -497,6 +538,9 @@ static long __bpf_get_stack(struct pt_regs *regs, >>>> struct task_struct *task, >>>> if (may_fault) >>>> rcu_read_unlock(); >>>> + if (!trace_in) >>>> + bpf_put_perf_callchain(rctx); >>>> + >>>> if (user_build_id) >>>> stack_map_get_build_id_offset(buf, trace_nr, user, may_fault); >>> >>> Hi Peter, >>> >>> As Alexei said, the patch needs your ack, please review again, thanks. >>> >> >> ping... > > Peter, if I understand correctly, this will go through bpf-next tree, > but it would be great if you could take a look and confirm this > overall is not broken. Thanks! > >> >> -- >> Best Regards >> Tao Chen Hi Andrii, Peter It appears that the code does not require a rebase, and the latest CI build is valid. Looking forward to your response. Thanks. CI has tested the following submission: Status: SUCCESS Name: [RESEND,bpf-next,v7,0/2] Pass external callchain entry to get_perf_callchain Patchwork: https://patchwork.kernel.org/project/netdevbpf/list/?series=1034091&state=* Matrix: https://github.com/kernel-patches/bpf/actions/runs/21051611369 -- Best Regards Tao Chen