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 fnext_task 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. [1] https://lkml.kernel.org/r/20180915160423.ga31...@redhat.com Suggested-by: Oleg Nesterov <o...@redhat.com> Signed-off-by: Eric W. Biederman <ebied...@xmission.com> --- fs/proc/fd.c | 17 +++++------------ 1 file changed, 5 insertions(+), 12 deletions(-) diff --git a/fs/proc/fd.c b/fs/proc/fd.c index abfdcb21cc79..d9fee5390fd7 100644 --- a/fs/proc/fd.c +++ b/fs/proc/fd.c @@ -218,7 +218,6 @@ 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) @@ -226,22 +225,18 @@ 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++, ctx->pos++) { struct file *f; struct fd_data data; char name[10 + 1]; unsigned int len; - f = fcheck_files(files, fd); + f = fnext_task(p, &fd); + ctx->pos = fd; if (!f) - continue; + break; data.mode = f->f_mode; rcu_read_unlock(); data.fd = fd; @@ -250,13 +245,11 @@ 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; -- 2.25.0
