Messages in this thread Patch in this message | | | Date | Tue, 17 Jul 2018 11:02:45 +0200 | From | Jiri Olsa <> | Subject | Re: [PATCH 1/4] perf tools: Fix struct comm_str removal crash |
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On Tue, Jul 17, 2018 at 10:49:40AM +0900, Namhyung Kim wrote: > Hi Jiri, > > On Mon, Jul 16, 2018 at 12:29:34PM +0200, Jiri Olsa wrote: > > On Sun, Jul 15, 2018 at 10:08:27PM +0900, Namhyung Kim wrote: > > > > SNIP > > > > > > Because thread 2 first decrements the refcnt and only after then it > > > > removes the struct comm_str from the list, the thread 1 can find this > > > > object on the list with refcnt equls to 0 and hit the assert. > > > > > > > > This patch fixes the thread 2 path, by removing the struct comm_str > > > > FIRST from the list and only AFTER calling comm_str__put on it. This > > > > way the thread 1 finds only valid objects on the list. > > > > > > I'm not sure we can unconditionally remove the comm_str from the tree. > > > It should be removed only if refcount is going to zero IMHO. > > > Otherwise it could end up having multiple comm_str entry for a same > > > name. > > > > right, but it wouldn't crash ;-) > > > > how about attached change, that actualy deals with the refcnt > > race I'm running the tests now, seems ok so far > > I think we can keep if the refcount is back to non-zero. What about this? > (not tested..) > > > static struct comm_str *comm_str__get(cs) > { > if (cs) > refcount_inc_no_warn(&cs->refcnt); // should be added > return cs; > } > > static void comm_str__put(cs) > { > if (cs && refcount_dec_and_test(&cs->refcnt)) { > down_write(&comm_str_lock); > /* might race with comm_str__findnew() */ > if (!refcount_read(&cs->refcnt)) { > rb_erase(&cs->rb_node, &comm_str_root); > zfree(&cs->str); > free(cs); > } > up_write(&comm_str_lock); > } > }
yea, it's more possitive than my patch I'm testing attached patch, looks good so far
thanks, jirka
--- diff --git a/tools/include/linux/refcount.h b/tools/include/linux/refcount.h index 36cb29bc57c2..11e2be6f68a0 100644 --- a/tools/include/linux/refcount.h +++ b/tools/include/linux/refcount.h @@ -109,6 +109,14 @@ static inline void refcount_inc(refcount_t *r) REFCOUNT_WARN(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n"); } +/* + * Pure refs increase without any chec/warn. + */ +static inline void refcount_inc_no_warn(refcount_t *r) +{ + atomic_inc(&r->refs); +} + /* * Similar to atomic_dec_and_test(), it will WARN on underflow and fail to * decrement when saturated at UINT_MAX. diff --git a/tools/perf/util/comm.c b/tools/perf/util/comm.c index 7798a2cc8a86..a2e338cf29d7 100644 --- a/tools/perf/util/comm.c +++ b/tools/perf/util/comm.c @@ -21,7 +21,7 @@ static struct rw_semaphore comm_str_lock = {.lock = PTHREAD_RWLOCK_INITIALIZER,} static struct comm_str *comm_str__get(struct comm_str *cs) { if (cs) - refcount_inc(&cs->refcnt); + refcount_inc_no_warn(&cs->refcnt); return cs; } @@ -29,10 +29,12 @@ static void comm_str__put(struct comm_str *cs) { if (cs && refcount_dec_and_test(&cs->refcnt)) { down_write(&comm_str_lock); - rb_erase(&cs->rb_node, &comm_str_root); + if (refcount_read(&cs->refcnt) == 0) { + rb_erase(&cs->rb_node, &comm_str_root); + zfree(&cs->str); + free(cs); + } up_write(&comm_str_lock); - zfree(&cs->str); - free(cs); } }
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