From: Muchun Song <songmuchun@bytedance.com>
To: adobriyan@gmail.com, ast@kernel.org, daniel@iogearbox.net,
kafai@fb.com, songliubraving@fb.com, yhs@fb.com, andriin@fb.com,
john.fastabend@gmail.com, kpsingh@chromium.org
Cc: ebiederm@xmission.com, bernd.edlinger@hotmail.de,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
netdev@vger.kernel.org, bpf@vger.kernel.org,
Muchun Song <songmuchun@bytedance.com>
Subject: [PATCH] files: Use rcu lock to get the file structures for better performance
Date: Thu, 21 May 2020 20:38:35 +0800 [thread overview]
Message-ID: <20200521123835.70069-1-songmuchun@bytedance.com> (raw)
There is another safe way to get the file structure without
holding the files->file_lock. That is rcu lock, and this way
has better performance. So use the rcu lock instead of the
files->file_lock.
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
fs/proc/fd.c | 31 ++++++++++++++++++++++++-------
kernel/bpf/syscall.c | 17 +++++++++++------
kernel/kcmp.c | 15 ++++++++++-----
3 files changed, 45 insertions(+), 18 deletions(-)
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 81882a13212d3..5d5b0f091d32a 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -34,19 +34,27 @@ static int seq_show(struct seq_file *m, void *v)
if (files) {
unsigned int fd = proc_fd(m->private);
- spin_lock(&files->file_lock);
+ rcu_read_lock();
+again:
file = fcheck_files(files, fd);
if (file) {
- struct fdtable *fdt = files_fdtable(files);
+ struct fdtable *fdt;
+
+ if (!get_file_rcu(file)) {
+ /*
+ * we loop to catch the new file (or NULL
+ * pointer).
+ */
+ goto again;
+ }
+ fdt = files_fdtable(files);
f_flags = file->f_flags;
if (close_on_exec(fd, fdt))
f_flags |= O_CLOEXEC;
-
- get_file(file);
ret = 0;
}
- spin_unlock(&files->file_lock);
+ rcu_read_unlock();
put_files_struct(files);
}
@@ -160,14 +168,23 @@ static int proc_fd_link(struct dentry *dentry, struct path *path)
unsigned int fd = proc_fd(d_inode(dentry));
struct file *fd_file;
- spin_lock(&files->file_lock);
+ rcu_read_lock();
+again:
fd_file = fcheck_files(files, fd);
if (fd_file) {
+ if (!get_file_rcu(fd_file)) {
+ /*
+ * we loop to catch the new file
+ * (or NULL pointer).
+ */
+ goto again;
+ }
*path = fd_file->f_path;
path_get(&fd_file->f_path);
+ fput(fd_file);
ret = 0;
}
- spin_unlock(&files->file_lock);
+ rcu_read_unlock();
put_files_struct(files);
}
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 8608d6e1b0e0e..441c91378a1fc 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3451,14 +3451,19 @@ static int bpf_task_fd_query(const union bpf_attr *attr,
if (!files)
return -ENOENT;
- err = 0;
- spin_lock(&files->file_lock);
+ rcu_read_lock();
+again:
file = fcheck_files(files, fd);
- if (!file)
+ if (file) {
+ if (!get_file_rcu(file)) {
+ /* we loop to catch the new file (or NULL pointer) */
+ goto again;
+ }
+ err = 0;
+ } else {
err = -EBADF;
- else
- get_file(file);
- spin_unlock(&files->file_lock);
+ }
+ rcu_read_unlock();
put_files_struct(files);
if (err)
diff --git a/kernel/kcmp.c b/kernel/kcmp.c
index b3ff9288c6cc9..3b4f2a54186f2 100644
--- a/kernel/kcmp.c
+++ b/kernel/kcmp.c
@@ -120,13 +120,18 @@ static int kcmp_epoll_target(struct task_struct *task1,
if (!files)
return -EBADF;
- spin_lock(&files->file_lock);
+ rcu_read_lock();
+again:
filp_epoll = fcheck_files(files, slot.efd);
- if (filp_epoll)
- get_file(filp_epoll);
- else
+ if (filp_epoll) {
+ if (!get_file_rcu(filp_epoll)) {
+ /* we loop to catch the new file (or NULL pointer) */
+ goto again;
+ }
+ } else {
filp_tgt = ERR_PTR(-EBADF);
- spin_unlock(&files->file_lock);
+ }
+ rcu_read_unlock();
put_files_struct(files);
if (filp_epoll) {
--
2.11.0
next reply other threads:[~2020-05-21 12:39 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-21 12:38 Muchun Song [this message]
2020-05-21 15:21 ` [PATCH] files: Use rcu lock to get the file structures for better performance Matthew Wilcox
2020-05-21 16:06 ` [External] " Muchun Song
2020-05-21 16:16 ` Greg KH
2020-05-21 16:47 ` Matthew Wilcox
2020-05-22 7:52 ` [External] " Muchun Song
2020-05-22 11:43 ` Matthew Wilcox
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