[PATCH] tools: perf: add missing unlock to maps__insert error case

[PATCH] tools: perf: add missing unlock to maps__insert error case

[Cengiz Can]

`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@kernel.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?

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

Re: [PATCH] tools: perf: add missing unlock to maps__insert error case

[Arnaldo Carvalho de Melo]

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@kernel.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

Re: [PATCH] tools: perf: add missing unlock to maps__insert error case

[Arnaldo Carvalho de Melo]

Em Fri, Jan 31, 2020 at 09:38:58AM +0100, Arnaldo Carvalho de Melo escreveu:
> Em Mon, Jan 20, 2020 at 05:15:54PM +0300, Cengiz Can escreveu:
> > 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.

BTW, you forgot to add:

Fixes: a7c2b572e217 ("perf map_groups: Auto sort maps by name, if needed")

Which I did, and next time please CC the perf tools reviewers, as noted
in MAINTAINERS, the lines starting with R:.

- Arnaldo

[acme@quaco perf]$ grep -A21 "PERFORMANCE EVENTS SUBSYSTEM$" MAINTAINERS
PERFORMANCE EVENTS SUBSYSTEM
M:	Peter Zijlstra <peterz@infradead.org>
M:	Ingo Molnar <mingo@redhat.com>
M:	Arnaldo Carvalho de Melo <acme@kernel.org>
R:	Mark Rutland <mark.rutland@arm.com>
R:	Alexander Shishkin <alexander.shishkin@linux.intel.com>
R:	Jiri Olsa <jolsa@redhat.com>
R:	Namhyung Kim <namhyung@kernel.org>
L:	linux-kernel@vger.kernel.org
T:	git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git perf/core
S:	Supported
F:	kernel/events/*
F:	include/linux/perf_event.h
F:	include/uapi/linux/perf_event.h
F:	arch/*/kernel/perf_event*.c
F:	arch/*/kernel/*/perf_event*.c
F:	arch/*/kernel/*/*/perf_event*.c
F:	arch/*/include/asm/perf_event.h
F:	arch/*/kernel/perf_callchain.c
F:	arch/*/events/*
F:	arch/*/events/*/*
F:	tools/perf/
[acme@quaco perf]$

Re: [PATCH] tools: perf: add missing unlock to maps__insert error case

[Cengiz Can]

On January 31, 2020 11:43:46 Arnaldo Carvalho de Melo 
<arnaldo.melo@gmail.com> wrote:

> Em Fri, Jan 31, 2020 at 09:38:58AM +0100, Arnaldo Carvalho de Melo escreveu:
>> Em Mon, Jan 20, 2020 at 05:15:54PM +0300, Cengiz Can escreveu:
>>> 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.
>
> BTW, you forgot to add:
>
> Fixes: a7c2b572e217 ("perf map_groups: Auto sort maps by name, if needed")
>
> Which I did, and next time please CC the perf tools reviewers, as noted
> in MAINTAINERS, the lines starting with R:.

Missed that. Thank you for reminding and correction.

Cheers
>
> - Arnaldo
>
> [acme@quaco perf]$ grep -A21 "PERFORMANCE EVENTS SUBSYSTEM$" MAINTAINERS
> PERFORMANCE EVENTS SUBSYSTEM
> M: Peter Zijlstra <peterz@infradead.org>
> M: Ingo Molnar <mingo@redhat.com>
> M: Arnaldo Carvalho de Melo <acme@kernel.org>
> R: Mark Rutland <mark.rutland@arm.com>
> R: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> R: Jiri Olsa <jolsa@redhat.com>
> R: Namhyung Kim <namhyung@kernel.org>
> L: linux-kernel@vger.kernel.org
> T: git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git perf/core
> S: Supported
> F: kernel/events/*
> F: include/linux/perf_event.h
> F: include/uapi/linux/perf_event.h
> F: arch/*/kernel/perf_event*.c
> F: arch/*/kernel/*/perf_event*.c
> F: arch/*/kernel/*/*/perf_event*.c
> F: arch/*/include/asm/perf_event.h
> F: arch/*/kernel/perf_callchain.c
> F: arch/*/events/*
> F: arch/*/events/*/*
> F: tools/perf/
> [acme@quaco perf]$