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 5b17b61870e2f4b0a4fdc5c6039fbdb4ffb796df ]
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 Signed-off-by: Chuck Lever chuck.lever@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 c1a984f3c4df7..72c1525b4b3eb 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;