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Message-ID: <CAP-5=fWo2eM+aATScvQsBZKj7mZKug6HBW5bEw1Xp_Hqk3m3Vg@mail.gmail.com>
Date: Wed, 28 May 2025 10:55:45 -0700
From: Ian Rogers <irogers@...gle.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Athira Rajeev <atrajeev@...ux.vnet.ibm.com>, Bill Wendling <morbo@...gle.com>,
Chaitanya S Prakash <chaitanyas.prakash@....com>, Fei Lang <langfei@...wei.com>,
Howard Chu <howardchu95@...il.com>, Ingo Molnar <mingo@...hat.com>,
James Clark <james.clark@...aro.org>, Jiri Olsa <jolsa@...nel.org>,
Justin Stitt <justinstitt@...gle.com>, Kan Liang <kan.liang@...ux.intel.com>,
Mark Rutland <mark.rutland@....com>, Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Peter Zijlstra <peterz@...radead.org>,
Stephen Brennan <stephen.s.brennan@...cle.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 1/1] Revert "perf thread: Ensure comm_lock held for comm_list"
On Wed, May 28, 2025 at 8:58 AM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> Hi Ian,
>
> This one had hit perf-tools-next, so I'm reverting it till we
> figure out, since I'm trying to finish processing patches real soon now
> for this window, to give it some time to soak in linux-next.
>
> I noticed that sometimes when trying to exit 'perf top' it just
> sat there, so doing a bisect I ended up on this one, had no time to
> properly investigate it.
Hi Arnaldo,
I believe it is fixed by:
https://lore.kernel.org/lkml/20250528032637.198960-8-irogers@google.com/
I was actually trying to repro a DEBUG=1 issue I'd seen in `perf top`
with this assert failing:
https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/maps.c?h=perf-tools-next#n80
```
assert(RC_CHK_EQUAL(map__kmap(map)->kmaps, maps));
```
but no dice on that - I suspect it has something to do with modules or
BPF or something.
Anyway, with the patch above `perf top` for me I wasn't able to make
it crash even when being aggressive and running with both address and
memory sanitizer.
Thanks,
Ian
> - Arnaldo
>
> On Wed, May 28, 2025 at 12:57:11PM -0300, Arnaldo Carvalho de Melo wrote:
> > This reverts commit 8f454c95817d15ee529d58389612ea4b34f5ffb3.
> >
> > 'perf top' is freezing on exit sometimes, bisected to this one, revert.
> >
> > Cc: Adrian Hunter <adrian.hunter@...el.com>
> > Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> > Cc: Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
> > Cc: Bill Wendling <morbo@...gle.com>
> > Cc: Chaitanya S Prakash <chaitanyas.prakash@....com>
> > Cc: Fei Lang <langfei@...wei.com>
> > Cc: Howard Chu <howardchu95@...il.com>
> > Cc: Ian Rogers <irogers@...gle.com>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: James Clark <james.clark@...aro.org>
> > Cc: Jiri Olsa <jolsa@...nel.org>
> > Cc: Justin Stitt <justinstitt@...gle.com>
> > Cc: Kan Liang <kan.liang@...ux.intel.com>
> > Cc: Mark Rutland <mark.rutland@....com>
> > Cc: Namhyung Kim <namhyung@...nel.org>
> > Cc: Nathan Chancellor <nathan@...nel.org>
> > Cc: Nick Desaulniers <nick.desaulniers+lkml@...il.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Stephen Brennan <stephen.s.brennan@...cle.com>
> > Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> > ---
> > tools/perf/util/comm.c | 2 --
> > tools/perf/util/thread.c | 17 ++++-------------
> > tools/perf/util/thread.h | 9 ++++-----
> > 3 files changed, 8 insertions(+), 20 deletions(-)
> >
> > diff --git a/tools/perf/util/comm.c b/tools/perf/util/comm.c
> > index 9880247a2c3364cb..8aa456d7c2cd2d74 100644
> > --- a/tools/perf/util/comm.c
> > +++ b/tools/perf/util/comm.c
> > @@ -24,7 +24,6 @@ static struct comm_strs {
> > static void comm_strs__remove_if_last(struct comm_str *cs);
> >
> > static void comm_strs__init(void)
> > - NO_THREAD_SAFETY_ANALYSIS /* Inherently single threaded due to pthread_once. */
> > {
> > init_rwsem(&_comm_strs.lock);
> > _comm_strs.capacity = 16;
> > @@ -120,7 +119,6 @@ static void comm_strs__remove_if_last(struct comm_str *cs)
> > }
> >
> > static struct comm_str *__comm_strs__find(struct comm_strs *comm_strs, const char *str)
> > - SHARED_LOCKS_REQUIRED(comm_strs->lock)
> > {
> > struct comm_str **result;
> >
> > diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
> > index c202b98b36c29215..415c0e5d1e751a47 100644
> > --- a/tools/perf/util/thread.c
> > +++ b/tools/perf/util/thread.c
> > @@ -41,7 +41,6 @@ int thread__init_maps(struct thread *thread, struct machine *machine)
> > }
> >
> > struct thread *thread__new(pid_t pid, pid_t tid)
> > - NO_THREAD_SAFETY_ANALYSIS /* Allocation/creation is inherently single threaded. */
> > {
> > RC_STRUCT(thread) *_thread = zalloc(sizeof(*_thread));
> > struct thread *thread;
> > @@ -203,29 +202,22 @@ int thread__set_namespaces(struct thread *thread, u64 timestamp,
> >
> > struct comm *thread__comm(struct thread *thread)
> > {
> > - struct comm *res = NULL;
> > + if (list_empty(thread__comm_list(thread)))
> > + return NULL;
> >
> > - down_read(thread__comm_lock(thread));
> > - if (!list_empty(thread__comm_list(thread)))
> > - res = list_first_entry(thread__comm_list(thread), struct comm, list);
> > - up_read(thread__comm_lock(thread));
> > - return res;
> > + return list_first_entry(thread__comm_list(thread), struct comm, list);
> > }
> >
> > struct comm *thread__exec_comm(struct thread *thread)
> > {
> > struct comm *comm, *last = NULL, *second_last = NULL;
> >
> > - down_read(thread__comm_lock(thread));
> > list_for_each_entry(comm, thread__comm_list(thread), list) {
> > - if (comm->exec) {
> > - up_read(thread__comm_lock(thread));
> > + if (comm->exec)
> > return comm;
> > - }
> > second_last = last;
> > last = comm;
> > }
> > - up_read(thread__comm_lock(thread));
> >
> > /*
> > * 'last' with no start time might be the parent's comm of a synthesized
> > @@ -241,7 +233,6 @@ struct comm *thread__exec_comm(struct thread *thread)
> >
> > static int ____thread__set_comm(struct thread *thread, const char *str,
> > u64 timestamp, bool exec)
> > - EXCLUSIVE_LOCKS_REQUIRED(thread__comm_lock(thread))
> > {
> > struct comm *new, *curr = thread__comm(thread);
> >
> > diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
> > index 56e08c8ae005e82b..cd574a896418ac94 100644
> > --- a/tools/perf/util/thread.h
> > +++ b/tools/perf/util/thread.h
> > @@ -236,15 +236,14 @@ static inline struct rw_semaphore *thread__namespaces_lock(struct thread *thread
> > return &RC_CHK_ACCESS(thread)->namespaces_lock;
> > }
> >
> > -static inline struct rw_semaphore *thread__comm_lock(struct thread *thread)
> > +static inline struct list_head *thread__comm_list(struct thread *thread)
> > {
> > - return &RC_CHK_ACCESS(thread)->comm_lock;
> > + return &RC_CHK_ACCESS(thread)->comm_list;
> > }
> >
> > -static inline struct list_head *thread__comm_list(struct thread *thread)
> > - SHARED_LOCKS_REQUIRED(thread__comm_lock(thread))
> > +static inline struct rw_semaphore *thread__comm_lock(struct thread *thread)
> > {
> > - return &RC_CHK_ACCESS(thread)->comm_list;
> > + return &RC_CHK_ACCESS(thread)->comm_lock;
> > }
> >
> > static inline u64 thread__db_id(const struct thread *thread)
> > --
> > 2.49.0
> >
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