linux-kernel - Re: [PATCH] mm: mmap_lock: fix disabling preemption directly

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Date:   Tue, 20 Jul 2021 13:50:24 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>, cuibixuan@...wei.com,
        Vlastimil Babka <vbabka@...e.cz>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: mmap_lock: fix disabling preemption directly

On Tue, Jul 20, 2021 at 12:43 AM Muchun Song <songmuchun@...edance.com> wrote:
>
> The commit 832b50725373 ("mm: mmap_lock: use local locks instead of
> disabling preemption") fix a bug by using local locks. But commit
> d01079f3d0c0 ("mm/mmap_lock: remove dead code for !CONFIG_TRACING
> configurations") changes those lines to original version. I guess
> it is introduced by the conflicts fixing on merging.
>
> Fixes: d01079f3d0c0 ("mm/mmap_lock: remove dead code for !CONFIG_TRACING configurations")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>

Reviewed-by: Yang Shi <shy828301@...il.com>

> ---
>  mm/mmap_lock.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c
> index f5852a058ce0..1854850b4b89 100644
> --- a/mm/mmap_lock.c
> +++ b/mm/mmap_lock.c
> @@ -156,14 +156,14 @@ static inline void put_memcg_path_buf(void)
>  #define TRACE_MMAP_LOCK_EVENT(type, mm, ...)                                   \
>         do {                                                                   \
>                 const char *memcg_path;                                        \
> -               preempt_disable();                                             \
> +               local_lock(&memcg_paths.lock);                                 \
>                 memcg_path = get_mm_memcg_path(mm);                            \
>                 trace_mmap_lock_##type(mm,                                     \
>                                        memcg_path != NULL ? memcg_path : "",   \
>                                        ##__VA_ARGS__);                         \
>                 if (likely(memcg_path != NULL))                                \
>                         put_memcg_path_buf();                                  \
> -               preempt_enable();                                              \
> +               local_unlock(&memcg_paths.lock);                               \
>         } while (0)
>
>  #else /* !CONFIG_MEMCG */
> --
> 2.11.0
>