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([2a02:8109:a307:d900:699e:f085:b19f:def1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488d531f1f9sm372374165e9.1.2026.04.13.10.32.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Apr 2026 10:32:34 -0700 (PDT) Message-ID: Date: Mon, 13 Apr 2026 18:32:33 +0100 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next v9 2/6] bpf: Add bpf_prog_run_array_sleepable() To: Alexei Starovoitov Cc: bpf , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin Lau , Kernel Team , Eduard , Kumar Kartikeya Dwivedi , Peter Zijlstra , Steven Rostedt , Mykyta Yatsenko References: <20260410-sleepable_tracepoints-v9-0-e719e664e84c@meta.com> <20260410-sleepable_tracepoints-v9-2-e719e664e84c@meta.com> <76e88c11-fc18-42e1-920e-e0965b984689@gmail.com> Content-Language: en-US From: Mykyta Yatsenko In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 4/13/26 5:25 PM, Alexei Starovoitov wrote: > On Mon, Apr 13, 2026 at 5:55 AM Mykyta Yatsenko > wrote: >> >> >> >> On 4/10/26 11:55 PM, Alexei Starovoitov wrote: >>> On Fri, Apr 10, 2026 at 10:09 AM Mykyta Yatsenko >>> wrote: >>>> >>>> From: Mykyta Yatsenko >>>> >>>> Add bpf_prog_run_array_sleepable() for running BPF program arrays >>>> on faultable tracepoints. Unlike bpf_prog_run_array_uprobe(), it >>>> includes per-program recursion checking for private stack safety >>>> and hardcodes is_uprobe to false. >>>> >>>> Keep bpf_prog_run_array_uprobe() unchanged for uprobe callers. >>>> >>>> Acked-by: Kumar Kartikeya Dwivedi >>>> Signed-off-by: Mykyta Yatsenko >>>> --- >>>> include/linux/bpf.h | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++ >>>> 1 file changed, 50 insertions(+) >>>> >>>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h >>>> index 0136a108d083..4e166accab35 100644 >>>> --- a/include/linux/bpf.h >>>> +++ b/include/linux/bpf.h >>>> @@ -3077,6 +3077,56 @@ void bpf_dynptr_set_null(struct bpf_dynptr_kern *ptr); >>>> void bpf_dynptr_set_rdonly(struct bpf_dynptr_kern *ptr); >>>> void bpf_prog_report_arena_violation(bool write, unsigned long addr, unsigned long fault_ip); >>>> >>>> +static __always_inline u32 >>>> +bpf_prog_run_array_sleepable(const struct bpf_prog_array *array, >>>> + const void *ctx, bpf_prog_run_fn run_prog) >>>> +{ >>>> + const struct bpf_prog_array_item *item; >>>> + struct bpf_prog *prog; >>>> + struct bpf_run_ctx *old_run_ctx; >>>> + struct bpf_trace_run_ctx run_ctx; >>>> + u32 ret = 1; >>>> + >>>> + might_fault(); >>>> + RCU_LOCKDEP_WARN(!rcu_read_lock_trace_held(), "no rcu lock held"); >>>> + >>>> + if (unlikely(!array)) >>>> + return ret; >>>> + >>>> + migrate_disable(); >>>> + >>>> + run_ctx.is_uprobe = false; >>>> + >>>> + old_run_ctx = bpf_set_run_ctx(&run_ctx.run_ctx); >>>> + item = &array->items[0]; >>>> + while ((prog = READ_ONCE(item->prog))) { >>>> + if (!prog->sleepable) >>>> + rcu_read_lock(); >>>> + >>>> + /* Per-prog recursion check to enable private stack. */ >>>> + if (unlikely(!bpf_prog_get_recursion_context(prog))) { >>> >>> from sashiko >>> >>>> + old_run_ctx = bpf_set_run_ctx(&run_ctx.run_ctx); >>>> + item = &array->items[0]; >>>> + while ((prog = READ_ONCE(item->prog))) { >>>> + if (!prog->sleepable) >>>> + rcu_read_lock(); >>>> + >>>> + /* Per-prog recursion check to enable private stack. */ >>>> + if (unlikely(!bpf_prog_get_recursion_context(prog))) { >>> >>> Can this cause a panic by dereferencing dummy_bpf_prog.prog.active? >>> When a program is detached from a BPF array and memory allocation for the new >>> array fails, bpf_prog_array_delete_safe() replaces the detached program with >>> &dummy_bpf_prog.prog as a fallback. >>> Because dummy_bpf_prog is a statically allocated placeholder, its prog.active >>> field is uninitialized (NULL). >>> If prog is dummy_bpf_prog.prog, bpf_prog_get_recursion_context() will >>> dereference prog->active as a per-CPU pointer, accessing offset 0 in the >>> per-CPU area and causing memory corruption or a panic. >>> Should there be an explicit check to skip dummy_bpf_prog.prog here? >> >> Looks like a real issue, thanks. I think the best solution is to add >> valid `prog->active` field for the dummy_bpf_prog.prog so we don't need >> to maintain special branches and can rely on the being a valid bpf_prog. > > No. Don't copy paste from claude. Ask it to do the home work. > This was already discussed on the list. > I mean 'oh it's NULL let's add it'. It was similar issue elsewhere > and solved differently. Actually claude suggested to simply check if prog == dummy_bpf_prog.prog, similarly to how it's done in kernel/bpf/core.c (for example function bpf_prog_array_copy_core()), but to me adding a valid `active` field sounds like a more future proof solution.