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Message-Id: <20200817220425.9389-10-ebiederm@xmission.com>
Date: Mon, 17 Aug 2020 17:04:18 -0500
From: "Eric W. Biederman" <ebiederm@...ssion.com>
To: linux-kernel@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org, criu@...nvz.org,
bpf@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <christian.brauner@...ntu.com>,
Oleg Nesterov <oleg@...hat.com>,
Cyrill Gorcunov <gorcunov@...il.com>,
Jann Horn <jann@...jh.net>, Kees Cook <keescook@...omium.org>,
Daniel P. Berrangé <berrange@...hat.com>,
Jeff Layton <jlayton@...hat.com>,
Miklos Szeredi <miklos@...redi.hu>,
Matthew Wilcox <willy@...ian.org>,
"J. Bruce Fields" <bfields@...ldses.org>,
Matthew Wilcox <matthew@....cx>,
Trond Myklebust <trond.myklebust@....uio.no>,
Chris Wright <chrisw@...hat.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
Andrii Nakryiko <andriin@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...omium.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 10/17] proc/fd: In proc_readfd_common use fnext_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.
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.GA31461@redhat.com
Suggested-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Eric W. Biederman <ebiederm@...ssion.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
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