netdev - Re: [PATCH] tools: perf: add missing unlock to maps_

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Date:   Fri, 31 Jan 2020 09:38:58 +0100
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Cengiz Can <cengiz@...nel.wtf>
Cc:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH] tools: perf: add missing unlock to maps__insert error
 case

Em Mon, Jan 20, 2020 at 05:15:54PM +0300, Cengiz Can escreveu:
> `tools/perf/util/map.c` has a function named `maps__insert` that
> acquires a write lock if its in multithread context.
> 
> Even though this lock is released when function successfully completes,
> there's a branch that is executed when `maps_by_name == NULL` that
> returns from this function without releasing the write lock.
> 
> Added an `up_write` to release the lock when this happens.
> 
> Signed-off-by: Cengiz Can <cengiz@...nel.wtf>
> ---
> 
> Hello Arnaldo,
> 
> I'm not exactly sure about the order that we must call up_write here.
> 
> Please tell me if the `__maps__free_maps_by_name` frees the
> `rw_semaphore`. If that's the case, should we change the order to unlock and free?

No it doesn't free the rw_semaphore, that is in 'struct maps', what is
being freed is just something protected by rw_semaphore,
maps->maps_by_name, so your patch is right and I'm applying it, thanks.

- Arnaldo
 
> Thanks!
> 
>  tools/perf/util/map.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
> index fdd5bddb3075..f67960bedebb 100644
> --- a/tools/perf/util/map.c
> +++ b/tools/perf/util/map.c
> @@ -549,6 +549,7 @@ void maps__insert(struct maps *maps, struct map *map)
> 
>  			if (maps_by_name == NULL) {
>  				__maps__free_maps_by_name(maps);
> +				up_write(&maps->lock);
>  				return;
>  			}
> 
> --
> 2.25.0
> 

-- 

- Arnaldo