[PATCH 10/39] get rid of perf_fget_light(), convert kernel/events/core.c to CLASS(fd)

viro
2024-07-30T05:14:56Z

From: Al Viro <viro@zeniv.linux.org.uk>

Lift fdget() and fdput() out of perf_fget_light(), turning it into
is_perf_file(struct fd f). The life gets easier in both callers
if we do fdget() unconditionally, including the case when we are
given -1 instead of a descriptor - that avoids a reassignment in
perf_event_open(2) and it avoids a nasty temptation in _perf_ioctl()
where we must *not* lift output_event out of scope for output.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
kernel/events/core.c | 49 +++++++++++++++-----------------------------
1 file changed, 16 insertions(+), 33 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index fd2ac9c7fd77..dae815c30514 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5895,18 +5895,9 @@ EXPORT_SYMBOL_GPL(perf_event_period);

static const struct file_operations perf_fops;

-static inline int perf_fget_light(int fd, struct fd *p)
+static inline bool is_perf_file(struct fd f)
{
- struct fd f = fdget(fd);
- if (!fd_file(f))
- return -EBADF;
-
- if (fd_file(f)->f_op != &perf_fops) {
- fdput(f);
- return -EBADF;
- }
- *p = f;
- return 0;
+ return !fd_empty(f) && fd_file(f)->f_op == &perf_fops;
}

static int perf_event_set_output(struct perf_event *event,
@@ -5954,20 +5945,14 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon

case PERF_EVENT_IOC_SET_OUTPUT:
{
- int ret;
+ CLASS(fd, output)(arg); // arg == -1 => empty
+ struct perf_event *output_event = NULL;
if (arg != -1) {
- struct perf_event *output_event;
- struct fd output;
- ret = perf_fget_light(arg, &output);
- if (ret)
- return ret;
+ if (!is_perf_file(output))
+ return -EBADF;
output_event = fd_file(output)->private_data;
- ret = perf_event_set_output(event, output_event);
- fdput(output);
- } else {
- ret = perf_event_set_output(event, NULL);
}
- return ret;
+ return perf_event_set_output(event, output_event);
}

case PERF_EVENT_IOC_SET_FILTER:
@@ -12474,7 +12459,6 @@ SYSCALL_DEFINE5(perf_event_open,
struct perf_event_attr attr;
struct perf_event_context *ctx;
struct file *event_file = NULL;
- struct fd group = EMPTY_FD;
struct task_struct *task = NULL;
struct pmu *pmu;
int event_fd;
@@ -12545,10 +12529,12 @@ SYSCALL_DEFINE5(perf_event_open,
if (event_fd < 0)
return event_fd;

+ CLASS(fd, group)(group_fd); // group_fd == -1 => empty
if (group_fd != -1) {
- err = perf_fget_light(group_fd, &group);
- if (err)
+ if (!is_perf_file(group)) {
+ err = -EBADF;
goto err_fd;
+ }
group_leader = fd_file(group)->private_data;
if (flags & PERF_FLAG_FD_OUTPUT)
output_event = group_leader;
@@ -12560,7 +12546,7 @@ SYSCALL_DEFINE5(perf_event_open,
task = find_lively_task_by_vpid(pid);
if (IS_ERR(task)) {
err = PTR_ERR(task);
- goto err_group_fd;
+ goto err_fd;
}
}

@@ -12827,12 +12813,11 @@ SYSCALL_DEFINE5(perf_event_open,
mutex_unlock(&current->perf_event_mutex);

/*
- * Drop the reference on the group_event after placing the
- * new event on the sibling_list. This ensures destruction
- * of the group leader will find the pointer to itself in
- * perf_group_detach().
+ * File reference in group guarantees that group_leader has been
+ * kept alive until we place the new event on the sibling_list.
+ * This ensures destruction of the group leader will find
+ * the pointer to itself in perf_group_detach().
*/
- fdput(group);
fd_install(event_fd, event_file);
return event_fd;

@@ -12851,8 +12836,6 @@ SYSCALL_DEFINE5(perf_event_open,
err_task:
if (task)
put_task_struct(task);
-err_group_fd:
- fdput(group);
err_fd:
put_unused_fd(event_fd);
return err;
--
2.39.2