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authorEric W. Biederman <ebiederm@xmission.com>2020-11-20 17:14:23 -0600
committerEric W. Biederman <ebiederm@xmission.com>2020-12-10 12:39:48 -0600
commit439be32656035d3239fd56f9b83353ec06cb3b45 (patch)
tree019377cd0b079b710aded2fdec028ed85016e455 /fs/proc/fd.c
parentb48845af0152d790a54b8ab78cc2b7c07485fc98 (diff)
downloadlinux-439be32656035d3239fd56f9b83353ec06cb3b45.tar.bz2
proc/fd: In proc_fd_link use fget_task
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. Simplifying proc_fd_link is a little bit tricky. It is necessary to know that there is a reference to fd_f ile while path_get is running. This reference can either be guaranteed to exist either by locking the fdtable as the code currently does or by taking a reference on the file in question. Use fget_task to remove the need for get_files_struct and to take a reference to file in question. [1] https://lkml.kernel.org/r/20180915160423.GA31461@redhat.com Suggested-by: Oleg Nesterov <oleg@redhat.com> v1: https://lkml.kernel.org/r/20200817220425.9389-8-ebiederm@xmission.com Link: https://lkml.kernel.org/r/20201120231441.29911-6-ebiederm@xmission.com Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Diffstat (limited to 'fs/proc/fd.c')
-rw-r--r--fs/proc/fd.c13
1 files changed, 3 insertions, 10 deletions
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 81882a13212d..d58960f6ee52 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -146,29 +146,22 @@ static const struct dentry_operations tid_fd_dentry_operations = {
static int proc_fd_link(struct dentry *dentry, struct path *path)
{
- struct files_struct *files = NULL;
struct task_struct *task;
int ret = -ENOENT;
task = get_proc_task(d_inode(dentry));
if (task) {
- files = get_files_struct(task);
- put_task_struct(task);
- }
-
- if (files) {
unsigned int fd = proc_fd(d_inode(dentry));
struct file *fd_file;
- spin_lock(&files->file_lock);
- fd_file = fcheck_files(files, fd);
+ fd_file = fget_task(task, fd);
if (fd_file) {
*path = fd_file->f_path;
path_get(&fd_file->f_path);
ret = 0;
+ fput(fd_file);
}
- spin_unlock(&files->file_lock);
- put_files_struct(files);
+ put_task_struct(task);
}
return ret;