perf/core improvements and fixes

index c9a6dc173e74..b0c2b5c5d337 100644
@@ -233,17 +233,6 @@ int db_export__symbol(struct db_export *dbe, struct symbol *sym,
 	return 0;
 }
 
-static struct thread *get_main_thread(struct machine *machine, struct thread *thread)
-{
-	if (thread->pid_ == thread->tid)
-		return thread__get(thread);
-
-	if (thread->pid_ == -1)
-		return NULL;
-
-	return machine__find_thread(machine, thread->pid_, thread->pid_);
-}
-
 static int db_ids_from_al(struct db_export *dbe, struct addr_location *al,
 			  u64 *dso_db_id, u64 *sym_db_id, u64 *offset)
 {

@@ -382,7 +371,7 @@ int db_export__sample(struct db_export *dbe, union perf_event *event,
 	if (err)
 		return err;
 
-	main_thread = get_main_thread(al->machine, thread);
+	main_thread = thread__main_thread(al->machine, thread);
 	if (main_thread)
 		comm = machine__thread_exec_comm(al->machine, main_thread);
 

index 45fcb715a36b..ada58e6070bf 100644
@@ -265,3 +265,14 @@ void thread__find_cpumode_addr_location(struct thread *thread,
 			break;
 	}
 }
+
+struct thread *thread__main_thread(struct machine *machine, struct thread *thread)
+{
+	if (thread->pid_ == thread->tid)
+		return thread__get(thread);
+
+	if (thread->pid_ == -1)
+		return NULL;
+
+	return machine__find_thread(machine, thread->pid_, thread->pid_);
+}

index 45fba13c800b..08fcb14cf637 100644
@@ -81,6 +81,8 @@ void thread__insert_map(struct thread *thread, struct map *map);
 int thread__fork(struct thread *thread, struct thread *parent, u64 timestamp);
 size_t thread__fprintf(struct thread *thread, FILE *fp);
 
+struct thread *thread__main_thread(struct machine *machine, struct thread *thread);
+
 void thread__find_addr_map(struct thread *thread,
 			   u8 cpumode, enum map_type type, u64 addr,
 			   struct addr_location *al);

index 6b87be908790..0e43355c7aad 100644
@@ -1076,7 +1076,7 @@ extern void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct
 extern struct perf_callchain_entry *
 get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
 		   u32 max_stack, bool crosstask, bool add_mark);
-extern int get_callchain_buffers(void);
+extern int get_callchain_buffers(int max_stack);
 extern void put_callchain_buffers(void);
 
 extern int sysctl_perf_event_max_stack;

index 36ce552cf6a9..c66a485a24ac 100644
@@ -276,6 +276,9 @@ enum perf_event_read_format {
 
 /*
  * Hardware event_id to monitor via a performance monitoring event:
+ *
+ * @sample_max_stack: Max number of frame pointers in a callchain,
+ *		      should be < /proc/sys/kernel/perf_event_max_stack
  */
 struct perf_event_attr {
 

@@ -385,7 +388,8 @@ struct perf_event_attr {
 	 * Wakeup watermark for AUX area
 	 */
 	__u32	aux_watermark;
-	__u32	__reserved_2;	/* align to __u64 */
+	__u16	sample_max_stack;
+	__u16	__reserved_2;	/* align to __u64 */
 };
 
 #define perf_flags(attr)	(*(&(attr)->read_format + 1))

index a82d7605db3f..f1de5c1a2af6 100644
@@ -99,7 +99,7 @@ static struct bpf_map *stack_map_alloc(union bpf_attr *attr)
 	if (err)
 		goto free_smap;
 
-	err = get_callchain_buffers();
+	err = get_callchain_buffers(sysctl_perf_event_max_stack);
 	if (err)
 		goto free_smap;
 

index 179ef4640964..e9fdb5203de5 100644
@@ -104,7 +104,7 @@ fail:
 	return -ENOMEM;
 }
 
-int get_callchain_buffers(void)
+int get_callchain_buffers(int event_max_stack)
 {
 	int err = 0;
 	int count;

@@ -121,6 +121,15 @@ int get_callchain_buffers(void)
 		/* If the allocation failed, give up */
 		if (!callchain_cpus_entries)
 			err = -ENOMEM;
+		/*
+		 * If requesting per event more than the global cap,
+		 * return a different error to help userspace figure
+		 * this out.
+		 *
+		 * And also do it here so that we have &callchain_mutex held.
+		 */
+		if (event_max_stack > sysctl_perf_event_max_stack)
+			err = -EOVERFLOW;
 		goto exit;
 	}
 

@@ -174,11 +183,12 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs)
 	bool user   = !event->attr.exclude_callchain_user;
 	/* Disallow cross-task user callchains. */
 	bool crosstask = event->ctx->task && event->ctx->task != current;
+	const u32 max_stack = event->attr.sample_max_stack;
 
 	if (!kernel && !user)
 		return NULL;
 
-	return get_perf_callchain(regs, 0, kernel, user, sysctl_perf_event_max_stack, crosstask, true);
+	return get_perf_callchain(regs, 0, kernel, user, max_stack, crosstask, true);
 }
 
 struct perf_callchain_entry *

index 050a290c72c7..79363f298445 100644
@@ -8843,7 +8843,7 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 
 	if (!event->parent) {
 		if (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) {
-			err = get_callchain_buffers();
+			err = get_callchain_buffers(attr->sample_max_stack);
 			if (err)
 				goto err_addr_filters;
 		}

@@ -9165,6 +9165,9 @@ SYSCALL_DEFINE5(perf_event_open,
 			return -EINVAL;
 	}
 
+	if (!attr.sample_max_stack)
+		attr.sample_max_stack = sysctl_perf_event_max_stack;
+
 	/*
 	 * In cgroup mode, the pid argument is used to pass the fd
 	 * opened to the cgroup directory in cgroupfs. The cpu argument

index 65e2a4f7cb4e..a70f6b54eb92 100644
@@ -94,6 +94,7 @@ struct callchain_param {
 	enum perf_call_graph_mode record_mode;
 	u32			dump_size;
 	enum chain_mode 	mode;
+	u16			max_stack;
 	u32			print_limit;
 	double			min_percent;
 	sort_chain_func_t	sort;

index 02c177d14c8d..245ac503f211 100644
@@ -572,6 +572,8 @@ void perf_evsel__config_callchain(struct perf_evsel *evsel,
 
 	perf_evsel__set_sample_bit(evsel, CALLCHAIN);
 
+	attr->sample_max_stack = param->max_stack;
+
 	if (param->record_mode == CALLCHAIN_LBR) {
 		if (!opts->branch_stack) {
 			if (attr->exclude_user) {

@@ -635,7 +637,8 @@ static void apply_config_terms(struct perf_evsel *evsel,
 	struct perf_event_attr *attr = &evsel->attr;
 	struct callchain_param param;
 	u32 dump_size = 0;
-	char *callgraph_buf = NULL;
+	int max_stack = 0;
+	const char *callgraph_buf = NULL;
 
 	/* callgraph default */
 	param.record_mode = callchain_param.record_mode;

@@ -662,6 +665,9 @@ static void apply_config_terms(struct perf_evsel *evsel,
 		case PERF_EVSEL__CONFIG_TERM_STACK_USER:
 			dump_size = term->val.stack_user;
 			break;
+		case PERF_EVSEL__CONFIG_TERM_MAX_STACK:
+			max_stack = term->val.max_stack;
+			break;
 		case PERF_EVSEL__CONFIG_TERM_INHERIT:
 			/*
 			 * attr->inherit should has already been set by

@@ -677,7 +683,12 @@ static void apply_config_terms(struct perf_evsel *evsel,
 	}
 
 	/* User explicitly set per-event callgraph, clear the old setting and reset. */
-	if ((callgraph_buf != NULL) || (dump_size > 0)) {
+	if ((callgraph_buf != NULL) || (dump_size > 0) || max_stack) {
+		if (max_stack) {
+			param.max_stack = max_stack;
+			if (callgraph_buf == NULL)
+				callgraph_buf = "fp";
+		}
 
 		/* parse callgraph parameters */
 		if (callgraph_buf != NULL) {

@@ -1329,6 +1340,7 @@ int perf_event_attr__fprintf(FILE *fp, struct perf_event_attr *attr,
 	PRINT_ATTRf(clockid, p_signed);
 	PRINT_ATTRf(sample_regs_intr, p_hex);
 	PRINT_ATTRf(aux_watermark, p_unsigned);
+	PRINT_ATTRf(sample_max_stack, p_unsigned);
 
 	return ret;
 }

index c1f10159804c..028412b32d5a 100644
@@ -44,6 +44,7 @@ enum {
 	PERF_EVSEL__CONFIG_TERM_CALLGRAPH,
 	PERF_EVSEL__CONFIG_TERM_STACK_USER,
 	PERF_EVSEL__CONFIG_TERM_INHERIT,
+	PERF_EVSEL__CONFIG_TERM_MAX_STACK,
 	PERF_EVSEL__CONFIG_TERM_MAX,
 };
 

@@ -56,6 +57,7 @@ struct perf_evsel_config_term {
 		bool	time;
 		char	*callgraph;
 		u64	stack_user;
+		int	max_stack;
 		bool	inherit;
 	} val;
 };

index bcbc983d4b12..89d40bb425e1 100644
@@ -900,6 +900,7 @@ static const char *config_term_names[__PARSE_EVENTS__TERM_TYPE_NR] = {
 	[PARSE_EVENTS__TERM_TYPE_STACKSIZE]		= "stack-size",
 	[PARSE_EVENTS__TERM_TYPE_NOINHERIT]		= "no-inherit",
 	[PARSE_EVENTS__TERM_TYPE_INHERIT]		= "inherit",
+	[PARSE_EVENTS__TERM_TYPE_MAX_STACK]		= "max-stack",
 };
 
 static bool config_term_shrinked;

@@ -995,6 +996,9 @@ do {									   \
 	case PARSE_EVENTS__TERM_TYPE_NAME:
 		CHECK_TYPE_VAL(STR);
 		break;
+	case PARSE_EVENTS__TERM_TYPE_MAX_STACK:
+		CHECK_TYPE_VAL(NUM);
+		break;
 	default:
 		err->str = strdup("unknown term");
 		err->idx = term->err_term;

@@ -1040,6 +1044,7 @@ static int config_term_tracepoint(struct perf_event_attr *attr,
 	case PARSE_EVENTS__TERM_TYPE_STACKSIZE:
 	case PARSE_EVENTS__TERM_TYPE_INHERIT:
 	case PARSE_EVENTS__TERM_TYPE_NOINHERIT:
+	case PARSE_EVENTS__TERM_TYPE_MAX_STACK:
 		return config_term_common(attr, term, err);
 	default:
 		if (err) {

@@ -1109,6 +1114,9 @@ do {								\
 		case PARSE_EVENTS__TERM_TYPE_NOINHERIT:
 			ADD_CONFIG_TERM(INHERIT, inherit, term->val.num ? 0 : 1);
 			break;
+		case PARSE_EVENTS__TERM_TYPE_MAX_STACK:
+			ADD_CONFIG_TERM(MAX_STACK, max_stack, term->val.num);
+			break;
 		default:
 			break;
 		}

index d740c3ca9a1d..46c05ccd5dfe 100644
@@ -68,6 +68,7 @@ enum {
 	PARSE_EVENTS__TERM_TYPE_STACKSIZE,
 	PARSE_EVENTS__TERM_TYPE_NOINHERIT,
 	PARSE_EVENTS__TERM_TYPE_INHERIT,
+	PARSE_EVENTS__TERM_TYPE_MAX_STACK,
 	__PARSE_EVENTS__TERM_TYPE_NR,
 };
 

index 2335b2824d8a..43d30ea87b7e 100644
@@ -593,6 +593,7 @@ do { 						\
 	if (bswap_safe(f, 0))			\
 		attr->f = bswap_##sz(attr->f);	\
 } while(0)
+#define bswap_field_16(f) bswap_field(f, 16)
 #define bswap_field_32(f) bswap_field(f, 32)
 #define bswap_field_64(f) bswap_field(f, 64)
 

@@ -608,6 +609,7 @@ do { 						\
 	bswap_field_64(sample_regs_user);
 	bswap_field_32(sample_stack_user);
 	bswap_field_32(aux_watermark);
+	bswap_field_16(sample_max_stack);
 
 	/*
 	 * After read_format are bitfields. Check read_format because

index 357f1b13b5ae..2e5567c94e09 100644
@@ -62,6 +62,8 @@ int perf_event__synth_time_conv(const struct perf_event_mmap_page *pc,
 	struct perf_tsc_conversion tc;
 	int err;
 
+	if (!pc)
+		return 0;
 	err = perf_read_tsc_conversion(pc, &tc);
 	if (err == -EOPNOTSUPP)
 		return 0;

index dc3fcb597e4c..d4cf1b0c88f9 100644
@@ -655,6 +655,13 @@ perf_event__synth_time_conv(const struct perf_event_mmap_page *pc __maybe_unused
 	return 0;
 }
 
+static const struct perf_event_mmap_page *record__pick_pc(struct record *rec)
+{
+	if (rec->evlist && rec->evlist->mmap && rec->evlist->mmap[0].base)
+		return rec->evlist->mmap[0].base;
+	return NULL;
+}
+
 static int record__synthesize(struct record *rec)
 {
 	struct perf_session *session = rec->session;

@@ -692,7 +699,7 @@ static int record__synthesize(struct record *rec)
 		}
 	}
 
-	err = perf_event__synth_time_conv(rec->evlist->mmap[0].base, tool,
+	err = perf_event__synth_time_conv(record__pick_pc(rec), tool,
 					  process_synthesized_event, machine);
 	if (err)
 		goto out;

index e82ba90cc969..50d7b80987c0 100644
@@ -462,9 +462,9 @@ int perf_evlist__alloc_pollfd(struct perf_evlist *evlist)
 	return 0;
 }
 
-static int __perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd, int idx)
+static int __perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd, int idx, short revent)
 {
-	int pos = fdarray__add(&evlist->pollfd, fd, POLLIN | POLLERR | POLLHUP);
+	int pos = fdarray__add(&evlist->pollfd, fd, revent | POLLERR | POLLHUP);
 	/*
 	 * Save the idx so that when we filter out fds POLLHUP'ed we can
 	 * close the associated evlist->mmap[] entry.

@@ -480,7 +480,7 @@ static int __perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd, int idx
 
 int perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd)
 {
-	return __perf_evlist__add_pollfd(evlist, fd, -1);
+	return __perf_evlist__add_pollfd(evlist, fd, -1, POLLIN);
 }
 
 static void perf_evlist__munmap_filtered(struct fdarray *fda, int fd)

@@ -983,15 +983,28 @@ static int __perf_evlist__mmap(struct perf_evlist *evlist, int idx,
 	return 0;
 }
 
+static bool
+perf_evlist__should_poll(struct perf_evlist *evlist __maybe_unused,
+			 struct perf_evsel *evsel)
+{
+	if (evsel->overwrite)
+		return false;
+	return true;
+}
+
 static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int idx,
 				       struct mmap_params *mp, int cpu,
 				       int thread, int *output)
 {
 	struct perf_evsel *evsel;
+	int revent;
 
 	evlist__for_each(evlist, evsel) {
 		int fd;
 
+		if (evsel->overwrite != (evlist->overwrite && evlist->backward))
+			continue;
+
 		if (evsel->system_wide && thread)
 			continue;
 

@@ -1008,6 +1021,8 @@ static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int idx,
 			perf_evlist__mmap_get(evlist, idx);
 		}
 
+		revent = perf_evlist__should_poll(evlist, evsel) ? POLLIN : 0;
+
 		/*
 		 * The system_wide flag causes a selected event to be opened
 		 * always without a pid.  Consequently it will never get a

@@ -1016,7 +1031,7 @@ static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int idx,
 		 * Therefore don't add it for polling.
 		 */
 		if (!evsel->system_wide &&
-		    __perf_evlist__add_pollfd(evlist, fd, idx) < 0) {
+		    __perf_evlist__add_pollfd(evlist, fd, idx, revent) < 0) {
 			perf_evlist__mmap_put(evlist, idx);
 			return -1;
 		}

index 50d7b80987c0..58ede3257c61 100644
@@ -856,9 +856,11 @@ static void perf_evlist__mmap_get(struct perf_evlist *evlist, int idx)
 
 static void perf_evlist__mmap_put(struct perf_evlist *evlist, int idx)
 {
-	BUG_ON(atomic_read(&evlist->mmap[idx].refcnt) == 0);
+	struct perf_mmap *md = &evlist->mmap[idx];
+
+	BUG_ON(md->base && atomic_read(&md->refcnt) == 0);
 
-	if (atomic_dec_and_test(&evlist->mmap[idx].refcnt))
+	if (atomic_dec_and_test(&md->refcnt))
 		__perf_evlist__munmap(evlist, idx);
 }
 

index 58ede3257c61..719729ef9d7c 100644
@@ -777,7 +777,7 @@ broken_event:
 	return event;
 }
 
-union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
+union perf_event *perf_evlist__mmap_read_forward(struct perf_evlist *evlist, int idx)
 {
 	struct perf_mmap *md = &evlist->mmap[idx];
 	u64 head;

@@ -832,6 +832,13 @@ perf_evlist__mmap_read_backward(struct perf_evlist *evlist, int idx)
 	return perf_mmap__read(md, false, start, end, &md->prev);
 }
 
+union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
+{
+	if (!evlist->backward)
+		return perf_evlist__mmap_read_forward(evlist, idx);
+	return perf_evlist__mmap_read_backward(evlist, idx);
+}
+
 void perf_evlist__mmap_read_catchup(struct perf_evlist *evlist, int idx)
 {
 	struct perf_mmap *md = &evlist->mmap[idx];

index d740fb877ab6..68cb1361c97c 100644
@@ -131,6 +131,8 @@ struct perf_sample_id *perf_evlist__id2sid(struct perf_evlist *evlist, u64 id);
 
 union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx);
 
+union perf_event *perf_evlist__mmap_read_forward(struct perf_evlist *evlist,
+						 int idx);
 union perf_event *perf_evlist__mmap_read_backward(struct perf_evlist *evlist,
 						  int idx);
 void perf_evlist__mmap_read_catchup(struct perf_evlist *evlist, int idx);

index 0e636c4339b8..b0a035fc87b3 100644
@@ -85,7 +85,8 @@ int fdarray__add(struct fdarray *fda, int fd, short revents)
 }
 
 int fdarray__filter(struct fdarray *fda, short revents,
-		    void (*entry_destructor)(struct fdarray *fda, int fd))
+		    void (*entry_destructor)(struct fdarray *fda, int fd, void *arg),
+		    void *arg)
 {
 	int fd, nr = 0;
 

@@ -95,7 +96,7 @@ int fdarray__filter(struct fdarray *fda, short revents,
 	for (fd = 0; fd < fda->nr; ++fd) {
 		if (fda->entries[fd].revents & revents) {
 			if (entry_destructor)
-				entry_destructor(fda, fd);
+				entry_destructor(fda, fd, arg);
 
 			continue;
 		}

index 45db01818f45..e87fd800fa8d 100644
@@ -34,7 +34,8 @@ void fdarray__delete(struct fdarray *fda);
 int fdarray__add(struct fdarray *fda, int fd, short revents);
 int fdarray__poll(struct fdarray *fda, int timeout);
 int fdarray__filter(struct fdarray *fda, short revents,
-		    void (*entry_destructor)(struct fdarray *fda, int fd));
+		    void (*entry_destructor)(struct fdarray *fda, int fd, void *arg),
+		    void *arg);
 int fdarray__grow(struct fdarray *fda, int extra);
 int fdarray__fprintf(struct fdarray *fda, FILE *fp);
 

index c809463edbe5..59dbd0550c51 100644
@@ -36,7 +36,7 @@ int test__fdarray__filter(int subtest __maybe_unused)
 	}
 
 	fdarray__init_revents(fda, POLLIN);
-	nr_fds = fdarray__filter(fda, POLLHUP, NULL);
+	nr_fds = fdarray__filter(fda, POLLHUP, NULL, NULL);
 	if (nr_fds != fda->nr_alloc) {
 		pr_debug("\nfdarray__filter()=%d != %d shouldn't have filtered anything",
 			 nr_fds, fda->nr_alloc);

@@ -44,7 +44,7 @@ int test__fdarray__filter(int subtest __maybe_unused)
 	}
 
 	fdarray__init_revents(fda, POLLHUP);
-	nr_fds = fdarray__filter(fda, POLLHUP, NULL);
+	nr_fds = fdarray__filter(fda, POLLHUP, NULL, NULL);
 	if (nr_fds != 0) {
 		pr_debug("\nfdarray__filter()=%d != %d, should have filtered all fds",
 			 nr_fds, fda->nr_alloc);

@@ -57,7 +57,7 @@ int test__fdarray__filter(int subtest __maybe_unused)
 
 	pr_debug("\nfiltering all but fda->entries[2]:");
 	fdarray__fprintf_prefix(fda, "before", stderr);
-	nr_fds = fdarray__filter(fda, POLLHUP, NULL);
+	nr_fds = fdarray__filter(fda, POLLHUP, NULL, NULL);
 	fdarray__fprintf_prefix(fda, " after", stderr);
 	if (nr_fds != 1) {
 		pr_debug("\nfdarray__filter()=%d != 1, should have left just one event", nr_fds);

@@ -78,7 +78,7 @@ int test__fdarray__filter(int subtest __maybe_unused)
 
 	pr_debug("\nfiltering all but (fda->entries[0], fda->entries[3]):");
 	fdarray__fprintf_prefix(fda, "before", stderr);
-	nr_fds = fdarray__filter(fda, POLLHUP, NULL);
+	nr_fds = fdarray__filter(fda, POLLHUP, NULL, NULL);
 	fdarray__fprintf_prefix(fda, " after", stderr);
 	if (nr_fds != 2) {
 		pr_debug("\nfdarray__filter()=%d != 2, should have left just two events",

index 719729ef9d7c..e0f30946ed1a 100644
@@ -483,7 +483,8 @@ int perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd)
 	return __perf_evlist__add_pollfd(evlist, fd, -1, POLLIN);
 }
 
-static void perf_evlist__munmap_filtered(struct fdarray *fda, int fd)
+static void perf_evlist__munmap_filtered(struct fdarray *fda, int fd,
+					 void *arg __maybe_unused)
 {
 	struct perf_evlist *evlist = container_of(fda, struct perf_evlist, pollfd);
 

@@ -493,7 +494,7 @@ static void perf_evlist__munmap_filtered(struct fdarray *fda, int fd)
 int perf_evlist__filter_pollfd(struct perf_evlist *evlist, short revents_and_mask)
 {
 	return fdarray__filter(&evlist->pollfd, revents_and_mask,
-			       perf_evlist__munmap_filtered);
+			       perf_evlist__munmap_filtered, NULL);
 }
 
 int perf_evlist__poll(struct perf_evlist *evlist, int timeout)

index 54c4ff2b1cee..a469346a305d 100644
@@ -1641,6 +1641,20 @@ static int find_matching_kcore(struct map *map, char *dir, size_t dir_sz)
 	return ret;
 }
 
+/*
+ * Use open(O_RDONLY) to check readability directly instead of access(R_OK)
+ * since access(R_OK) only checks with real UID/GID but open() use effective
+ * UID/GID and actual capabilities (e.g. /proc/kcore requires CAP_SYS_RAWIO).
+ */
+static bool filename__readable(const char *file)
+{
+	int fd = open(file, O_RDONLY);
+	if (fd < 0)
+		return false;
+	close(fd);
+	return true;
+}
+
 static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 {
 	u8 host_build_id[BUILD_ID_SIZE];

@@ -1668,7 +1682,6 @@ static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 	/* Use /proc/kallsyms if possible */
 	if (is_host) {
 		DIR *d;
-		int fd;
 
 		/* If no cached kcore go with /proc/kallsyms */
 		d = opendir(path);

@@ -1677,16 +1690,15 @@ static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 		closedir(d);
 
 		/*
-		 * Do not check the build-id cache, until we know we cannot use
-		 * /proc/kcore.
+		 * Do not check the build-id cache, unless we know we cannot use
+		 * /proc/kcore or module maps don't match to /proc/kallsyms.
+		 * To check readability of /proc/kcore, do not use access(R_OK)
+		 * since /proc/kcore requires CAP_SYS_RAWIO to read and access
+		 * can't check it.
 		 */
-		fd = open("/proc/kcore", O_RDONLY);
-		if (fd != -1) {
-			close(fd);
-			/* If module maps match go with /proc/kallsyms */
-			if (!validate_kcore_addresses("/proc/kallsyms", map))
-				goto proc_kallsyms;
-		}
+		if (filename__readable("/proc/kcore") &&
+		    !validate_kcore_addresses("/proc/kallsyms", map))
+			goto proc_kallsyms;
 
 		/* Find kallsyms in build-id cache with kcore */
 		if (!find_matching_kcore(map, path, sizeof(path)))

index a469346a305d..1df6092c8665 100644
@@ -1674,21 +1674,8 @@ static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 				 sizeof(host_build_id)) == 0)
 		is_host = dso__build_id_equal(dso, host_build_id);
 
-	build_id__sprintf(dso->build_id, sizeof(dso->build_id), sbuild_id);
-
-	scnprintf(path, sizeof(path), "%s/%s/%s", buildid_dir,
-		  DSO__NAME_KCORE, sbuild_id);
-
-	/* Use /proc/kallsyms if possible */
+	/* Try a fast path for /proc/kallsyms if possible */
 	if (is_host) {
-		DIR *d;
-
-		/* If no cached kcore go with /proc/kallsyms */
-		d = opendir(path);
-		if (!d)
-			goto proc_kallsyms;
-		closedir(d);
-
 		/*
 		 * Do not check the build-id cache, unless we know we cannot use
 		 * /proc/kcore or module maps don't match to /proc/kallsyms.

@@ -1699,18 +1686,24 @@ static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 		if (filename__readable("/proc/kcore") &&
 		    !validate_kcore_addresses("/proc/kallsyms", map))
 			goto proc_kallsyms;
-
-		/* Find kallsyms in build-id cache with kcore */
-		if (!find_matching_kcore(map, path, sizeof(path)))
-			return strdup(path);
-
-		goto proc_kallsyms;
 	}
 
+	build_id__sprintf(dso->build_id, sizeof(dso->build_id), sbuild_id);
+
 	/* Find kallsyms in build-id cache with kcore */
+	scnprintf(path, sizeof(path), "%s/%s/%s",
+		  buildid_dir, DSO__NAME_KCORE, sbuild_id);
+
 	if (!find_matching_kcore(map, path, sizeof(path)))
 		return strdup(path);
 
+	/* Use current /proc/kallsyms if possible */
+	if (is_host) {
+proc_kallsyms:
+		return strdup("/proc/kallsyms");
+	}
+
+	/* Finally, find a cache of kallsyms */
 	scnprintf(path, sizeof(path), "%s/%s/%s",
 		  buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
 

@@ -1721,9 +1714,6 @@ static char *dso__find_kallsyms(struct dso *dso, struct map *map)
 	}
 
 	return strdup(path);
-
-proc_kallsyms:
-	return strdup("/proc/kallsyms");
 }
 
 static int dso__load_kernel_sym(struct dso *dso, struct map *map,

index 67e5966503b2..67f986c8c378 100644
@@ -144,7 +144,32 @@ static int asnprintf(char **strp, size_t size, const char *fmt, ...)
 	return ret;
 }
 
-static char *build_id__filename(const char *sbuild_id, char *bf, size_t size)
+char *build_id_cache__kallsyms_path(const char *sbuild_id, char *bf,
+				    size_t size)
+{
+	bool is_alloc = !!bf;
+	bool retry_old = true;
+
+	asnprintf(&bf, size, "%s/%s/%s/kallsyms",
+		  buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
+retry:
+	if (!access(bf, F_OK))
+		return bf;
+	if (is_alloc)
+		free(bf);
+	if (retry_old) {
+		/* Try old style kallsyms cache */
+		asnprintf(&bf, size, "%s/%s/%s",
+			  buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
+		retry_old = false;
+		goto retry;
+	}
+
+	return NULL;
+}
+
+static char *build_id_cache__linkname(const char *sbuild_id, char *bf,
+				      size_t size)
 {
 	char *tmp = bf;
 	int ret = asnprintf(&bf, size, "%s/.build-id/%.2s/%s", buildid_dir,

@@ -154,23 +179,52 @@ static char *build_id__filename(const char *sbuild_id, char *bf, size_t size)
 	return bf;
 }
 
+static const char *build_id_cache__basename(bool is_kallsyms, bool is_vdso)
+{
+	return is_kallsyms ? "kallsyms" : (is_vdso ? "vdso" : "elf");
+}
+
 char *dso__build_id_filename(const struct dso *dso, char *bf, size_t size)
 {
-	char build_id_hex[SBUILD_ID_SIZE];
+	bool is_kallsyms = dso__is_kallsyms((struct dso *)dso);
+	bool is_vdso = dso__is_vdso((struct dso *)dso);
+	char sbuild_id[SBUILD_ID_SIZE];
+	char *linkname;
+	bool alloc = (bf == NULL);
+	int ret;
 
 	if (!dso->has_build_id)
 		return NULL;
 
-	build_id__sprintf(dso->build_id, sizeof(dso->build_id), build_id_hex);
-	return build_id__filename(build_id_hex, bf, size);
+	build_id__sprintf(dso->build_id, sizeof(dso->build_id), sbuild_id);
+	linkname = build_id_cache__linkname(sbuild_id, NULL, 0);
+	if (!linkname)
+		return NULL;
+
+	/* Check if old style build_id cache */
+	if (is_regular_file(linkname))
+		ret = asnprintf(&bf, size, "%s", linkname);
+	else
+		ret = asnprintf(&bf, size, "%s/%s", linkname,
+			 build_id_cache__basename(is_kallsyms, is_vdso));
+	if (ret < 0 || (!alloc && size < (unsigned int)ret))
+		bf = NULL;
+	free(linkname);
+
+	return bf;
 }
 
 bool dso__build_id_is_kmod(const struct dso *dso, char *bf, size_t size)
 {
-	char *id_name, *ch;
+	char *id_name = NULL, *ch;
 	struct stat sb;
+	char sbuild_id[SBUILD_ID_SIZE];
+
+	if (!dso->has_build_id)
+		goto err;
 
-	id_name = dso__build_id_filename(dso, bf, size);
+	build_id__sprintf(dso->build_id, sizeof(dso->build_id), sbuild_id);
+	id_name = build_id_cache__linkname(sbuild_id, NULL, 0);
 	if (!id_name)
 		goto err;
 	if (access(id_name, F_OK))

@@ -194,18 +248,14 @@ bool dso__build_id_is_kmod(const struct dso *dso, char *bf, size_t size)
 	if (ch - 3 < bf)
 		goto err;
 
+	free(id_name);
 	return strncmp(".ko", ch - 3, 3) == 0;
 err:
-	/*
-	 * If dso__build_id_filename work, get id_name again,
-	 * because id_name points to bf and is broken.
-	 */
-	if (id_name)
-		id_name = dso__build_id_filename(dso, bf, size);
 	pr_err("Invalid build id: %s\n", id_name ? :
 					 dso->long_name ? :
 					 dso->short_name ? :
 					 "[unknown]");
+	free(id_name);
 	return false;
 }
 

@@ -341,7 +391,8 @@ void disable_buildid_cache(void)
 }
 
 static char *build_id_cache__dirname_from_path(const char *name,
-					       bool is_kallsyms, bool is_vdso)
+					       bool is_kallsyms, bool is_vdso,
+					       const char *sbuild_id)
 {
 	char *realname = (char *)name, *filename;
 	bool slash = is_kallsyms || is_vdso;

@@ -352,8 +403,9 @@ static char *build_id_cache__dirname_from_path(const char *name,
 			return NULL;
 	}
 
-	if (asprintf(&filename, "%s%s%s", buildid_dir, slash ? "/" : "",
-		     is_vdso ? DSO__NAME_VDSO : realname) < 0)
+	if (asprintf(&filename, "%s%s%s%s%s", buildid_dir, slash ? "/" : "",
+		     is_vdso ? DSO__NAME_VDSO : realname,
+		     sbuild_id ? "/" : "", sbuild_id ?: "") < 0)
 		filename = NULL;
 
 	if (!slash)

@@ -368,7 +420,8 @@ int build_id_cache__list_build_ids(const char *pathname,
 	char *dir_name;
 	int ret = 0;
 
-	dir_name = build_id_cache__dirname_from_path(pathname, false, false);
+	dir_name = build_id_cache__dirname_from_path(pathname, false, false,
+						     NULL);
 	if (!dir_name)
 		return -ENOMEM;
 

@@ -385,7 +438,7 @@ int build_id_cache__add_s(const char *sbuild_id, const char *name,
 {
 	const size_t size = PATH_MAX;
 	char *realname = NULL, *filename = NULL, *dir_name = NULL,
-	     *linkname = zalloc(size), *targetname, *tmp;
+	     *linkname = zalloc(size), *tmp;
 	int err = -1;
 
 	if (!is_kallsyms) {

@@ -394,14 +447,22 @@ int build_id_cache__add_s(const char *sbuild_id, const char *name,
 			goto out_free;
 	}
 
-	dir_name = build_id_cache__dirname_from_path(name, is_kallsyms, is_vdso);
+	dir_name = build_id_cache__dirname_from_path(name, is_kallsyms,
+						     is_vdso, sbuild_id);
 	if (!dir_name)
 		goto out_free;
 
+	/* Remove old style build-id cache */
+	if (is_regular_file(dir_name))
+		if (unlink(dir_name))
+			goto out_free;
+
 	if (mkdir_p(dir_name, 0755))
 		goto out_free;
 
-	if (asprintf(&filename, "%s/%s", dir_name, sbuild_id) < 0) {
+	/* Save the allocated buildid dirname */
+	if (asprintf(&filename, "%s/%s", dir_name,
+		     build_id_cache__basename(is_kallsyms, is_vdso)) < 0) {
 		filename = NULL;
 		goto out_free;
 	}

@@ -415,7 +476,7 @@ int build_id_cache__add_s(const char *sbuild_id, const char *name,
 			goto out_free;
 	}
 
-	if (!build_id__filename(sbuild_id, linkname, size))
+	if (!build_id_cache__linkname(sbuild_id, linkname, size))
 		goto out_free;
 	tmp = strrchr(linkname, '/');
 	*tmp = '\0';

@@ -424,10 +485,10 @@ int build_id_cache__add_s(const char *sbuild_id, const char *name,
 		goto out_free;
 
 	*tmp = '/';
-	targetname = filename + strlen(buildid_dir) - 5;
-	memcpy(targetname, "../..", 5);
+	tmp = dir_name + strlen(buildid_dir) - 5;
+	memcpy(tmp, "../..", 5);
 
-	if (symlink(targetname, linkname) == 0)
+	if (symlink(tmp, linkname) == 0)
 		err = 0;
 out_free:
 	if (!is_kallsyms)

@@ -452,7 +513,7 @@ static int build_id_cache__add_b(const u8 *build_id, size_t build_id_size,
 bool build_id_cache__cached(const char *sbuild_id)
 {
 	bool ret = false;
-	char *filename = build_id__filename(sbuild_id, NULL, 0);
+	char *filename = build_id_cache__linkname(sbuild_id, NULL, 0);
 
 	if (filename && !access(filename, F_OK))
 		ret = true;

@@ -471,7 +532,7 @@ int build_id_cache__remove_s(const char *sbuild_id)
 	if (filename == NULL || linkname == NULL)
 		goto out_free;
 
-	if (!build_id__filename(sbuild_id, linkname, size))
+	if (!build_id_cache__linkname(sbuild_id, linkname, size))
 		goto out_free;
 
 	if (access(linkname, F_OK))

@@ -489,7 +550,7 @@ int build_id_cache__remove_s(const char *sbuild_id)
 	tmp = strrchr(linkname, '/') + 1;
 	snprintf(tmp, size - (tmp - linkname), "%s", filename);
 
-	if (unlink(linkname))
+	if (rm_rf(linkname))
 		goto out_free;
 
 	err = 0;

@@ -501,7 +562,7 @@ out_free:
 
 static int dso__cache_build_id(struct dso *dso, struct machine *machine)
 {
-	bool is_kallsyms = dso->kernel && dso->long_name[0] != '/';
+	bool is_kallsyms = dso__is_kallsyms(dso);
 	bool is_vdso = dso__is_vdso(dso);
 	const char *name = dso->long_name;
 	char nm[PATH_MAX];

index 64af3e20610d..e5435f46e48e 100644
@@ -14,6 +14,8 @@ struct dso;
 int build_id__sprintf(const u8 *build_id, int len, char *bf);
 int sysfs__sprintf_build_id(const char *root_dir, char *sbuild_id);
 int filename__sprintf_build_id(const char *pathname, char *sbuild_id);
+char *build_id_cache__kallsyms_path(const char *sbuild_id, char *bf,
+				    size_t size);
 
 char *dso__build_id_filename(const struct dso *dso, char *bf, size_t size);
 bool dso__build_id_is_kmod(const struct dso *dso, char *bf, size_t size);

index 0953280629cf..76d79d070e21 100644
@@ -349,6 +349,11 @@ static inline bool dso__is_kcore(struct dso *dso)
 	       dso->binary_type == DSO_BINARY_TYPE__GUEST_KCORE;
 }
 
+static inline bool dso__is_kallsyms(struct dso *dso)
+{
+	return dso->kernel && dso->long_name[0] != '/';
+}
+
 void dso__free_a2l(struct dso *dso);
 
 enum dso_type dso__type(struct dso *dso, struct machine *machine);

index 1df6092c8665..09c5c34ae38d 100644
@@ -1704,10 +1704,7 @@ proc_kallsyms:
 	}
 
 	/* Finally, find a cache of kallsyms */
-	scnprintf(path, sizeof(path), "%s/%s/%s",
-		  buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
-
-	if (access(path, F_OK)) {
+	if (!build_id_cache__kallsyms_path(sbuild_id, path, sizeof(path))) {
 		pr_err("No kallsyms or vmlinux with build-id %s was found\n",
 		       sbuild_id);
 		return NULL;