5.10-stable review patch. If anyone has any objections, please let me know.
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From: Eric W. Biederman ebiederm@xmission.com
[ Upstream commit 439be32656035d3239fd56f9b83353ec06cb3b45 ]
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 Signed-off-by: Chuck Lever chuck.lever@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/proc/fd.c | 13 +++---------- 1 file changed, 3 insertions(+), 10 deletions(-)
diff --git a/fs/proc/fd.c b/fs/proc/fd.c index 81882a13212d3..d58960f6ee524 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;