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 E02D1355814 for ; Thu, 14 May 2026 20:38:03 +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=1778791086; cv=none; b=Ph9aTX2DXPO0th9DgTnb9b78fM4chSWz60rNU/liGYPGB6KCAGobbZwBM9GgP8SNc4fXtGFgia3AhNVKXRrmuxqaYd6LsIgJjNB5qSSb+9MIdts98PSZagaQptieXhEGr0LChMyuPKEnsHtW9w8UbLNwO3gU1wp0BZ13tkMxcM0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778791086; c=relaxed/simple; bh=go01oXcceTeotLSc8FBnfn/ift3sy3rW0XxYWSob+oI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rZPTbanbjCgUaE5gLrsla4oS2aCtBnIy+iqWYFTlqBTvW6LBhmjZQw2O3g90hz1DFgAS2l9jlLVrIjM6W6oAJMPfe6XDu60UzLON3YmOOmsBdw+RgFw/qenSAAinpI/Mph2fUXz4AVK5FSL2V+jFb6NUXUJLmQ0i1oI8frhlyus= 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=k1w13OXd; 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="k1w13OXd" Message-ID: <3091f0f2-eaf0-469b-8221-55e8ef3c6812@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1778791081; 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=Z/h6ShPXwqAubj3ugdzXRuezfp6udXhwHKqFbqwWq08=; b=k1w13OXdmbqbua2Euz5iHCTjCOA4F/lYiMJiN2W9HtE4wkhBjxeu9IgEXxPGRUtnrkzCMP HDYPyoUfHSXv3V4NTjhdlLdpKFl4wY2iv5nJu3wh4nfAm6VVhgtgMceXIRtvEzjXDwaipa qZ6Pq9gPfUBw5KQ9wOr1Dl/NjQUaRtw= Date: Thu, 14 May 2026 13:37:43 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf v4 2/3] bpf: Avoid faultable build ID reads under mm locks To: bot+bpf-ci@kernel.org, ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, eddyz87@gmail.com, memxor@gmail.com Cc: puranjay@kernel.org, shakeel.butt@linux.dev, mykyta.yatsenko5@gmail.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, martin.lau@kernel.org, yonghong.song@linux.dev, clm@meta.com References: <20260514184727.1067141-3-ihor.solodrai@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Ihor Solodrai In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 5/14/26 12:37 PM, bot+bpf-ci@kernel.org wrote: >> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c >> index 4ef0fd06cea5..c1e96df360c3 100644 >> --- a/kernel/bpf/stackmap.c >> +++ b/kernel/bpf/stackmap.c >> @@ -9,6 +9,7 @@ >> #include >> #include >> #include >> +#include >> #include "percpu_freelist.h" >> #include "mmap_unlock_work.h" > > [ ... ] > >> @@ -158,6 +159,105 @@ static inline void stack_map_build_id_set_ip(struct bpf_stack_build_id *id) >> memset(id->build_id, 0, BUILD_ID_SIZE_MAX); >> } >> >> +struct stack_map_vma_lock { >> + bool vma_locked; >> + struct vm_area_struct *vma; >> + struct mm_struct *mm; >> +}; >> + >> +static struct vm_area_struct * >> +stack_map_lock_vma(struct stack_map_vma_lock *lock, unsigned long ip) >> +{ >> + struct mm_struct *mm = lock->mm; >> + struct vm_area_struct *vma; >> + >> + if (WARN_ON_ONCE(!mm)) >> + return NULL; >> + >> + vma = lock_vma_under_rcu(mm, ip); >> + if (vma) >> + goto vma_locked; >> + >> + if (!mmap_read_trylock(mm)) >> + return NULL; >> + >> + vma = vma_lookup(mm, ip); >> + if (!vma) { >> + mmap_read_unlock(mm); >> + return NULL; >> + } >> + >> +#ifdef CONFIG_PER_VMA_LOCK >> + if (!vma_start_read_locked(vma)) { >> + mmap_read_unlock(mm); >> + return NULL; >> + } >> + mmap_read_unlock(mm); >> +#else >> + mmap_read_unlock(mm); >> + return NULL; >> +#endif >> +vma_locked: >> + lock->vma_locked = true; >> + lock->vma = vma; >> + return vma; >> +} >> + >> +static void stack_map_unlock_vma(struct stack_map_vma_lock *lock) >> +{ >> + struct vm_area_struct *vma = lock->vma; >> + >> + if (lock->vma_locked) { >> + if (WARN_ON_ONCE(!vma)) >> + goto out; >> + vma_end_read(vma); >> + } >> +out: >> + lock->vma_locked = false; >> + lock->vma = NULL; >> +} >> + >> +static void stack_map_get_build_id_offset_sleepable(struct bpf_stack_build_id *id_offs, >> + u32 trace_nr) >> +{ >> + struct mm_struct *mm = current->mm; >> + struct stack_map_vma_lock lock = { >> + .vma_locked = false, >> + .vma = NULL, >> + .mm = mm, >> + }; >> + unsigned long vm_pgoff, vm_start; >> + struct vm_area_struct *vma; >> + struct file *file; >> + u64 ip; >> + >> + for (u32 i = 0; i < trace_nr; i++) { >> + ip = READ_ONCE(id_offs[i].ip); >> + vma = stack_map_lock_vma(&lock, ip); >> + if (!vma || !vma->vm_file) { >> + stack_map_build_id_set_ip(&id_offs[i]); >> + stack_map_unlock_vma(&lock); >> + continue; >> + } > > Is the vm_file check here correct for classifying anonymous VMAs? > Per mm-vma.md, vma->vm_file is not a reliable indicator of file-backed > status. Some anonymous VMAs carry a vm_file reference, such as private > mappings of /dev/zero set via vma_set_anonymous() which sets vm_ops > = NULL but leaves vm_file populated. > > The canonical test is vma_is_anonymous(vma) (checking !vma->vm_ops). > For a private /dev/zero mapping, this code would pass /dev/zero to > build_id_parse_file() instead of immediately falling back to the raw IP. > > This was flagged in v3 review by bot+bpf-ci@kernel.org and acknowledged > by the author as a minor edge case but left unchanged for consistency > with existing code elsewhere in stackmap.c: > > https://lore.kernel.org/bpf/1f275575e3c2309dc7b7f099c7e5cd47bb25182d94883ca0893cf4aaf03c954c@mail.kernel.org/ > > Should this be switched to vma_is_anonymous(), or is it preferable to > keep the current pattern and address it later across all of stackmap.c? I wonder why the bots are so concerned. If they get support of at least one human I'll respin with an additional patch adding vma_is_anonymous() checks. > >> + >> + file = get_file(vma->vm_file); >> + vm_pgoff = vma->vm_pgoff; >> + vm_start = vma->vm_start; >> + stack_map_unlock_vma(&lock); >> + >> + /* build_id_parse_file() may block on filesystem reads */ >> + if (build_id_parse_file(file, id_offs[i].build_id, NULL)) { >> + stack_map_build_id_set_ip(&id_offs[i]); >> + fput(file); >> + continue; >> + } >> + fput(file); >> + >> + id_offs[i].offset = (vm_pgoff << PAGE_SHIFT) + ip - vm_start; >> + id_offs[i].status = BPF_STACK_BUILD_ID_VALID; >> + } >> +} > > [ ... ] > >> @@ -178,6 +278,11 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, >> const char *prev_build_id; >> int i; >> >> + if (may_fault && has_user_ctx) { >> + stack_map_get_build_id_offset_sleepable(id_offs, trace_nr); >> + return; >> + } >> + >> /* If the irq_work is in use, fall back to report ips. Same >> * fallback is used for kernel stack (!user) on a stackmap with >> * build_id. > > > --- > AI reviewed your patch. Please fix the bug or email reply why it's not a bug. > See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md > > CI run summary: https://github.com/kernel-patches/bpf/actions/runs/25879521172