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Message-ID: <a7f085be-3819-46f3-9424-58da25e1891e@linux.dev>
Date: Thu, 6 Nov 2025 11:28:37 +0800
From: Tao Chen <chen.dylane@...ux.dev>
To: Yonghong Song <yonghong.song@...ux.dev>, peterz@...radead.org,
mingo@...hat.com, acme@...nel.org, namhyung@...nel.org,
mark.rutland@....com, alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
irogers@...gle.com, adrian.hunter@...el.com, kan.liang@...ux.intel.com,
song@...nel.org, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
martin.lau@...ux.dev, eddyz87@...il.com, john.fastabend@...il.com,
kpsingh@...nel.org, sdf@...ichev.me, haoluo@...gle.com
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 1/2] perf: Refactor get_perf_callchain
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 <peterz@...radead.org>
>> Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
>> ---
>> 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] <TASK>
> [ 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
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