netdev - Re: [PATCH v4 bpf-next 1/2] bpf: introduce helper bpf_find

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Message-ID: <46583fe9-ddb5-78c5-63c0-5338563b8ab1@fb.com>
Date:   Thu, 4 Nov 2021 16:28:01 -0700
From:   Yonghong Song <yhs@...com>
To:     Song Liu <songliubraving@...com>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>
CC:     <ast@...nel.org>, <daniel@...earbox.net>, <andrii@...nel.org>,
        <kernel-team@...com>, <kpsingh@...nel.org>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v4 bpf-next 1/2] bpf: introduce helper bpf_find_vma



On 11/4/21 2:31 PM, Song Liu wrote:
> In some profiler use cases, it is necessary to map an address to the
> backing file, e.g., a shared library. bpf_find_vma helper provides a
> flexible way to achieve this. bpf_find_vma maps an address of a task to
> the vma (vm_area_struct) for this address, and feed the vma to an callback
> BPF function. The callback function is necessary here, as we need to
> ensure mmap_sem is unlocked.
> 
> It is necessary to lock mmap_sem for find_vma. To lock and unlock mmap_sem
> safely when irqs are disable, we use the same mechanism as stackmap with
> build_id. Specifically, when irqs are disabled, the unlocked is postponed
> in an irq_work. Refactor stackmap.c so that the irq_work is shared among
> bpf_find_vma and stackmap helpers.
> 
> Reported-by: kernel test robot <lkp@...el.com>

You don't need the above "Reported-by".

> Signed-off-by: Song Liu <songliubraving@...com>

LGTM.

Acked-by: Yonghong Song <yhs@...com>