[PATCH v2 14/18] perf machine: Protect machines->guests rbtree with a rw_semaphore
From: Ian Rogers
Date: Tue Oct 27 2026 - 19:18:17 EST
Unlike struct dsos, struct maps, and struct threads, struct machines had
no lock protecting its machines->guests rbtree. Synchronizing access to
machines->guests is needed both for concurrent guest machine lookups and
so machines__shrink() can safely iterate guest machines using
down_read_trylock(&machines->lock).
Add a rw_semaphore lock to struct machines to synchronize access to the
machines->guests rbtree across machines__add(), machines__find(),
machines__set_comm_exec(), machines__process_guests(),
machines__set_id_hdr_size(), machines__fprintf_dsos(),
machines__fprintf_dsos_buildid(), machines__destroy_kernel_maps(), and
machines__for_each_thread(), and check for an existing guest machine PID
under write lock in machines__add().
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
tools/perf/util/machine.c | 42 +++++++++++++++++++++++++++++++++------
tools/perf/util/machine.h | 1 +
2 files changed, 37 insertions(+), 6 deletions(-)
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index cb9e34220036..fb83da8ef09b 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -237,6 +237,7 @@ int machines__init(struct machines *machines, struct perf_session *session)
{
int err = machine__init(&machines->host, "", HOST_KERNEL_ID);
+ init_rwsem(&machines->lock);
machines->session = session;
machines->host.machines = machines;
machines->guests = RB_ROOT_CACHED;
@@ -247,12 +248,13 @@ void machines__exit(struct machines *machines)
{
machine__exit(&machines->host);
/* XXX exit guest */
+ exit_rwsem(&machines->lock);
}
struct machine *machines__add(struct machines *machines, pid_t pid,
const char *root_dir)
{
- struct rb_node **p = &machines->guests.rb_root.rb_node;
+ struct rb_node **p;
struct rb_node *parent = NULL;
struct machine *pos, *machine = malloc(sizeof(*machine));
bool leftmost = true;
@@ -265,9 +267,17 @@ struct machine *machines__add(struct machines *machines, pid_t pid,
return NULL;
}
+ down_write(&machines->lock);
+ p = &machines->guests.rb_root.rb_node;
while (*p != NULL) {
parent = *p;
pos = rb_entry(parent, struct machine, rb_node);
+ if (pid == pos->pid) {
+ up_write(&machines->lock);
+ machine__exit(machine);
+ free(machine);
+ return pos;
+ }
if (pid < pos->pid)
p = &(*p)->rb_left;
else {
@@ -278,8 +288,8 @@ struct machine *machines__add(struct machines *machines, pid_t pid,
rb_link_node(&machine->rb_node, parent, p);
rb_insert_color_cached(&machine->rb_node, &machines->guests, leftmost);
-
machine->machines = machines;
+ up_write(&machines->lock);
return machine;
}
@@ -290,16 +300,18 @@ void machines__set_comm_exec(struct machines *machines, bool comm_exec)
machines->host.comm_exec = comm_exec;
+ down_read(&machines->lock);
for (nd = rb_first_cached(&machines->guests); nd; nd = rb_next(nd)) {
struct machine *machine = rb_entry(nd, struct machine, rb_node);
machine->comm_exec = comm_exec;
}
+ up_read(&machines->lock);
}
struct machine *machines__find(struct machines *machines, pid_t pid)
{
- struct rb_node **p = &machines->guests.rb_root.rb_node;
+ struct rb_node **p;
struct rb_node *parent = NULL;
struct machine *machine;
struct machine *default_machine = NULL;
@@ -307,6 +319,8 @@ struct machine *machines__find(struct machines *machines, pid_t pid)
if (pid == HOST_KERNEL_ID)
return &machines->host;
+ down_read(&machines->lock);
+ p = &machines->guests.rb_root.rb_node;
while (*p != NULL) {
parent = *p;
machine = rb_entry(parent, struct machine, rb_node);
@@ -314,11 +328,14 @@ struct machine *machines__find(struct machines *machines, pid_t pid)
p = &(*p)->rb_left;
else if (pid > machine->pid)
p = &(*p)->rb_right;
- else
+ else {
+ up_read(&machines->lock);
return machine;
+ }
if (!machine->pid)
default_machine = machine;
}
+ up_read(&machines->lock);
return default_machine;
}
@@ -464,10 +481,12 @@ void machines__process_guests(struct machines *machines,
{
struct rb_node *nd;
+ down_read(&machines->lock);
for (nd = rb_first_cached(&machines->guests); nd; nd = rb_next(nd)) {
struct machine *pos = rb_entry(nd, struct machine, rb_node);
process(pos, data);
}
+ up_read(&machines->lock);
}
void machines__set_id_hdr_size(struct machines *machines, u16 id_hdr_size)
@@ -477,11 +496,13 @@ void machines__set_id_hdr_size(struct machines *machines, u16 id_hdr_size)
machines->host.id_hdr_size = id_hdr_size;
+ down_read(&machines->lock);
for (node = rb_first_cached(&machines->guests); node;
node = rb_next(node)) {
machine = rb_entry(node, struct machine, rb_node);
machine->id_hdr_size = id_hdr_size;
}
+ up_read(&machines->lock);
return;
}
@@ -935,10 +956,12 @@ size_t machines__fprintf_dsos(struct machines *machines, FILE *fp)
struct rb_node *nd;
size_t ret = dsos__fprintf(&machines->host.dsos, fp);
+ down_read(&machines->lock);
for (nd = rb_first_cached(&machines->guests); nd; nd = rb_next(nd)) {
struct machine *pos = rb_entry(nd, struct machine, rb_node);
ret += dsos__fprintf(&pos->dsos, fp);
}
+ up_read(&machines->lock);
return ret;
}
@@ -955,10 +978,12 @@ size_t machines__fprintf_dsos_buildid(struct machines *machines, FILE *fp,
struct rb_node *nd;
size_t ret = machine__fprintf_dsos_buildid(&machines->host, fp, skip, parm);
+ down_read(&machines->lock);
for (nd = rb_first_cached(&machines->guests); nd; nd = rb_next(nd)) {
struct machine *pos = rb_entry(nd, struct machine, rb_node);
ret += machine__fprintf_dsos_buildid(pos, fp, skip, parm);
}
+ up_read(&machines->lock);
return ret;
}
@@ -1303,10 +1328,12 @@ int machines__create_guest_kernel_maps(struct machines *machines)
void machines__destroy_kernel_maps(struct machines *machines)
{
- struct rb_node *next = rb_first_cached(&machines->guests);
+ struct rb_node *next;
machine__destroy_kernel_maps(&machines->host);
+ down_write(&machines->lock);
+ next = rb_first_cached(&machines->guests);
while (next) {
struct machine *pos = rb_entry(next, struct machine, rb_node);
@@ -1314,6 +1341,7 @@ void machines__destroy_kernel_maps(struct machines *machines)
rb_erase_cached(&pos->rb_node, &machines->guests);
machine__delete(pos);
}
+ up_write(&machines->lock);
}
int machines__create_kernel_maps(struct machines *machines, pid_t pid)
@@ -3134,13 +3162,15 @@ int machines__for_each_thread(struct machines *machines,
if (rc != 0)
return rc;
+ down_read(&machines->lock);
for (nd = rb_first_cached(&machines->guests); nd; nd = rb_next(nd)) {
struct machine *machine = rb_entry(nd, struct machine, rb_node);
rc = machine__for_each_thread(machine, fn, priv);
if (rc != 0)
- return rc;
+ break;
}
+ up_read(&machines->lock);
return rc;
}
diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
index 973a59f7c26a..147ce343e370 100644
--- a/tools/perf/util/machine.h
+++ b/tools/perf/util/machine.h
@@ -151,6 +151,7 @@ typedef void (*machine__process_t)(struct machine *machine, void *data);
struct machines {
/** @session: back link to owning session if there is one. */
struct perf_session *session;
+ struct rw_semaphore lock;
struct machine host;
struct rb_root_cached guests;
};
--
2.56.0.313.g2479322e68-goog