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authorEric W. Biederman <ebiederm@xmission.com>2020-11-21 02:14:32 +0300
committerEric W. Biederman <ebiederm@xmission.com>2020-12-10 21:42:58 +0300
commit5b17b61870e2f4b0a4fdc5c6039fbdb4ffb796df (patch)
tree100057dc856347fe9536e0fd94c83838c5e29c39 /fs/proc
parente9a53aeb5e0a838f10fcea74235664e7ad5e6e1a (diff)
downloadlinux-5b17b61870e2f4b0a4fdc5c6039fbdb4ffb796df.tar.xz
proc/fd: In proc_readfd_common use task_lookup_next_fd_rcu
When discussing[1] exec and posix file locks it was realized that none of the callers of get_files_struct fundamentally needed to call get_files_struct, and that by switching them to helper functions instead it will both simplify their code and remove unnecessary increments of files_struct.count. Those unnecessary increments can result in exec unnecessarily unsharing files_struct which breaking posix locks, and it can result in fget_light having to fallback to fget reducing system performance. Using task_lookup_next_fd_rcu simplifies proc_readfd_common, by moving the checking for the maximum file descritor into the generic code, and by remvoing the need for capturing and releasing a reference on files_struct. As task_lookup_fd_rcu may update the fd ctx->pos has been changed to be the fd +2 after task_lookup_fd_rcu returns. [1] https://lkml.kernel.org/r/20180915160423.GA31461@redhat.com Suggested-by: Oleg Nesterov <oleg@redhat.com> Tested-by: Andy Lavr <andy.lavr@gmail.com> v1: https://lkml.kernel.org/r/20200817220425.9389-10-ebiederm@xmission.com Link: https://lkml.kernel.org/r/20201120231441.29911-15-ebiederm@xmission.com Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Diffstat (limited to 'fs/proc')
-rw-r--r--fs/proc/fd.c17
1 files changed, 5 insertions, 12 deletions
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index c1a984f3c4df..72c1525b4b3e 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -217,7 +217,6 @@ static int proc_readfd_common(struct file *file, struct dir_context *ctx,
instantiate_t instantiate)
{
struct task_struct *p = get_proc_task(file_inode(file));
- struct files_struct *files;
unsigned int fd;
if (!p)
@@ -225,22 +224,18 @@ static int proc_readfd_common(struct file *file, struct dir_context *ctx,
if (!dir_emit_dots(file, ctx))
goto out;
- files = get_files_struct(p);
- if (!files)
- goto out;
rcu_read_lock();
- for (fd = ctx->pos - 2;
- fd < files_fdtable(files)->max_fds;
- fd++, ctx->pos++) {
+ for (fd = ctx->pos - 2;; fd++) {
struct file *f;
struct fd_data data;
char name[10 + 1];
unsigned int len;
- f = files_lookup_fd_rcu(files, fd);
+ f = task_lookup_next_fd_rcu(p, &fd);
+ ctx->pos = fd + 2LL;
if (!f)
- continue;
+ break;
data.mode = f->f_mode;
rcu_read_unlock();
data.fd = fd;
@@ -249,13 +244,11 @@ static int proc_readfd_common(struct file *file, struct dir_context *ctx,
if (!proc_fill_cache(file, ctx,
name, len, instantiate, p,
&data))
- goto out_fd_loop;
+ goto out;
cond_resched();
rcu_read_lock();
}
rcu_read_unlock();
-out_fd_loop:
- put_files_struct(files);
out:
put_task_struct(p);
return 0;