| Message ID | 20230821200311.GA22497@redhat.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | bpf: task_group_seq_get_next: cleanup the usage of get/put_task_struct | expand |
| Context | Check | Description |
|---|---|---|
| bpf/vmtest-bpf-PR | fail | merge-conflict |
| netdev/tree_selection | success | Guessing tree name failed - patch did not apply |
On 8/21/23 13:03, Oleg Nesterov wrote: > get_pid_task() makes no sense, the code does put_task_struct() soon after. > Use find_task_by_pid_ns() instead of find_pid_ns + get_pid_task and kill > kill put_task_struct(), this allows to do get_task_struct() only once > before return. > > While at it, kill the unnecessary "if (!pid)" check in the "if (!*tid)" > block, this matches the next usage of find_pid_ns() + get_pid_task() in > this function. > > Signed-off-by: Oleg Nesterov <oleg@redhat.com> > --- > kernel/bpf/task_iter.c | 12 ++---------- > 1 file changed, 2 insertions(+), 10 deletions(-) > > diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c > index 4d1125108014..1589ec3faded 100644 > --- a/kernel/bpf/task_iter.c > +++ b/kernel/bpf/task_iter.c > @@ -42,9 +42,6 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm > if (!*tid) { > /* The first time, the iterator calls this function. */ > pid = find_pid_ns(common->pid, common->ns); > - if (!pid) > - return NULL; > - > task = get_pid_task(pid, PIDTYPE_TGID); > if (!task) > return NULL; > @@ -66,17 +63,12 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm > return task; > } > > - pid = find_pid_ns(common->pid_visiting, common->ns); > - if (!pid) > - return NULL; > - > - task = get_pid_task(pid, PIDTYPE_PID); > + task = find_task_by_pid_ns(common->pid_visiting, common->ns); > if (!task) > return NULL; > > retry: > next_task = next_thread(task); > - put_task_struct(task); It called get_task_struct() against this task to hold a refcount at the previous time calling this function. When will it release the refcount? > > saved_tid = *tid; > *tid = __task_pid_nr_ns(next_task, PIDTYPE_PID, common->ns); > @@ -88,7 +80,6 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm > return NULL; > } > > - get_task_struct(next_task); > common->pid_visiting = *tid; > > if (skip_if_dup_files && task->files == task->group_leader->files) { > @@ -96,6 +87,7 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm > goto retry; > } > > + get_task_struct(next_task); > return next_task; > } >
On 8/21/23 13:32, Kui-Feng Lee wrote: > > > On 8/21/23 13:03, Oleg Nesterov wrote: >> get_pid_task() makes no sense, the code does put_task_struct() soon >> after. >> Use find_task_by_pid_ns() instead of find_pid_ns + get_pid_task and kill >> kill put_task_struct(), this allows to do get_task_struct() only once >> before return. >> >> While at it, kill the unnecessary "if (!pid)" check in the "if (!*tid)" >> block, this matches the next usage of find_pid_ns() + get_pid_task() in >> this function. >> >> Signed-off-by: Oleg Nesterov <oleg@redhat.com> >> --- >> kernel/bpf/task_iter.c | 12 ++---------- >> 1 file changed, 2 insertions(+), 10 deletions(-) >> >> diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c >> index 4d1125108014..1589ec3faded 100644 >> --- a/kernel/bpf/task_iter.c >> +++ b/kernel/bpf/task_iter.c >> @@ -42,9 +42,6 @@ static struct task_struct >> *task_group_seq_get_next(struct bpf_iter_seq_task_comm >> if (!*tid) { >> /* The first time, the iterator calls this function. */ >> pid = find_pid_ns(common->pid, common->ns); >> - if (!pid) >> - return NULL; >> - >> task = get_pid_task(pid, PIDTYPE_TGID); >> if (!task) >> return NULL; >> @@ -66,17 +63,12 @@ static struct task_struct >> *task_group_seq_get_next(struct bpf_iter_seq_task_comm >> return task; >> } >> - pid = find_pid_ns(common->pid_visiting, common->ns); >> - if (!pid) >> - return NULL; >> - >> - task = get_pid_task(pid, PIDTYPE_PID); >> + task = find_task_by_pid_ns(common->pid_visiting, common->ns); >> if (!task) >> return NULL; >> retry: >> next_task = next_thread(task); >> - put_task_struct(task); > > It called get_task_struct() against this task to hold a refcount at the > previous time calling this function. When will it release the refcount? Oh! I missed the fact that the caller will handle it. > >> saved_tid = *tid; >> *tid = __task_pid_nr_ns(next_task, PIDTYPE_PID, common->ns); >> @@ -88,7 +80,6 @@ static struct task_struct >> *task_group_seq_get_next(struct bpf_iter_seq_task_comm >> return NULL; >> } >> - get_task_struct(next_task); >> common->pid_visiting = *tid; >> if (skip_if_dup_files && task->files == >> task->group_leader->files) { >> @@ -96,6 +87,7 @@ static struct task_struct >> *task_group_seq_get_next(struct bpf_iter_seq_task_comm >> goto retry; >> } >> + get_task_struct(next_task); >> return next_task; >> }
On 8/21/23 1:03 PM, Oleg Nesterov wrote: > get_pid_task() makes no sense, the code does put_task_struct() soon after. > Use find_task_by_pid_ns() instead of find_pid_ns + get_pid_task and kill > kill put_task_struct(), this allows to do get_task_struct() only once remove the duplicated 'kill' in the above. > before return. > > While at it, kill the unnecessary "if (!pid)" check in the "if (!*tid)" > block, this matches the next usage of find_pid_ns() + get_pid_task() in > this function. > > Signed-off-by: Oleg Nesterov <oleg@redhat.com> LGTM. Acked-by: Yonghong Song <yonghong.song@linux.dev>
On 08/21, Yonghong Song wrote: > > > On 8/21/23 1:03 PM, Oleg Nesterov wrote: > >get_pid_task() makes no sense, the code does put_task_struct() soon after. > >Use find_task_by_pid_ns() instead of find_pid_ns + get_pid_task and kill > >kill put_task_struct(), this allows to do get_task_struct() only once > > remove the duplicated 'kill' in the above. Done, > LGTM. > > Acked-by: Yonghong Song <yonghong.song@linux.dev> Thanks, I'll send V2 with your ack included in a minute. Oleg.
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c index 4d1125108014..1589ec3faded 100644 --- a/kernel/bpf/task_iter.c +++ b/kernel/bpf/task_iter.c @@ -42,9 +42,6 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm if (!*tid) { /* The first time, the iterator calls this function. */ pid = find_pid_ns(common->pid, common->ns); - if (!pid) - return NULL; - task = get_pid_task(pid, PIDTYPE_TGID); if (!task) return NULL; @@ -66,17 +63,12 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm return task; } - pid = find_pid_ns(common->pid_visiting, common->ns); - if (!pid) - return NULL; - - task = get_pid_task(pid, PIDTYPE_PID); + task = find_task_by_pid_ns(common->pid_visiting, common->ns); if (!task) return NULL; retry: next_task = next_thread(task); - put_task_struct(task); saved_tid = *tid; *tid = __task_pid_nr_ns(next_task, PIDTYPE_PID, common->ns); @@ -88,7 +80,6 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm return NULL; } - get_task_struct(next_task); common->pid_visiting = *tid; if (skip_if_dup_files && task->files == task->group_leader->files) { @@ -96,6 +87,7 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm goto retry; } + get_task_struct(next_task); return next_task; }
get_pid_task() makes no sense, the code does put_task_struct() soon after. Use find_task_by_pid_ns() instead of find_pid_ns + get_pid_task and kill kill put_task_struct(), this allows to do get_task_struct() only once before return. While at it, kill the unnecessary "if (!pid)" check in the "if (!*tid)" block, this matches the next usage of find_pid_ns() + get_pid_task() in this function. Signed-off-by: Oleg Nesterov <oleg@redhat.com> --- kernel/bpf/task_iter.c | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-)