From: "Eric W. Biederman" <ebiederm@xmission.com>
To: linux-kernel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org, criu@openvz.org,
bpf@vger.kernel.org,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Alexander Viro" <viro@zeniv.linux.org.uk>,
"Christian Brauner" <christian.brauner@ubuntu.com>,
"Oleg Nesterov" <oleg@redhat.com>,
"Cyrill Gorcunov" <gorcunov@gmail.com>,
"Jann Horn" <jann@thejh.net>, "Kees Cook" <keescook@chromium.org>,
"Daniel P. Berrangé" <berrange@redhat.com>,
"Jeff Layton" <jlayton@redhat.com>,
"Miklos Szeredi" <miklos@szeredi.hu>,
"Matthew Wilcox" <willy@debian.org>,
"J. Bruce Fields" <bfields@fieldses.org>,
"Matthew Wilcox" <matthew@wil.cx>,
"Trond Myklebust" <trond.myklebust@fys.uio.no>,
"Chris Wright" <chrisw@redhat.com>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Martin KaFai Lau" <kafai@fb.com>,
"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
"Andrii Nakryiko" <andriin@fb.com>,
"John Fastabend" <john.fastabend@gmail.com>,
"KP Singh" <kpsingh@chromium.org>,
"Eric W. Biederman" <ebiederm@xmission.com>
Subject: [PATCH 10/17] proc/fd: In proc_readfd_common use fnext_task
Date: Mon, 17 Aug 2020 17:04:18 -0500 [thread overview]
Message-ID: <20200817220425.9389-10-ebiederm@xmission.com> (raw)
In-Reply-To: <87ft8l6ic3.fsf@x220.int.ebiederm.org>
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@redhat.com>
Signed-off-by: Eric W. Biederman <ebiederm@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
next prev parent reply other threads:[~2020-08-17 22:10 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-17 22:03 exec: Move unshare_files and guarantee files_struct.count is correct Eric W. Biederman
2020-08-17 22:04 ` [PATCH 01/17] exec: Move unshare_files to fix posix file locking during exec Eric W. Biederman
2020-08-18 10:04 ` Christian Brauner
2020-08-17 22:04 ` [PATCH 02/17] exec: Simplify unshare_files Eric W. Biederman
2020-08-18 10:08 ` Christian Brauner
2020-08-17 22:04 ` [PATCH 03/17] exec: Remove reset_files_struct Eric W. Biederman
2020-08-18 10:09 ` Christian Brauner
2020-08-17 22:04 ` [PATCH 04/17] kcmp: In kcmp_epoll_target use fget_task Eric W. Biederman
2020-08-20 21:45 ` Cyrill Gorcunov
2020-08-17 22:04 ` [PATCH 05/17] bpf: In bpf_task_fd_query " Eric W. Biederman
2020-08-17 22:04 ` [PATCH 06/17] file: Implement fcheck_task Eric W. Biederman
2020-08-18 10:37 ` Christian Brauner
2020-08-17 22:04 ` [PATCH 07/17] proc/fd: In tid_fd_mode use fcheck_task Eric W. Biederman
2020-08-18 10:36 ` Christian Brauner
2020-08-17 22:04 ` [PATCH 08/17] proc/fd: In proc_fd_link " Eric W. Biederman
2020-08-18 10:36 ` Christian Brauner
2020-08-17 22:04 ` [PATCH 09/17] file: Implement fnext_task Eric W. Biederman
2020-08-17 23:54 ` Linus Torvalds
[not found] ` <875z9g7oln.fsf@x220.int.ebiederm.org>
2020-08-18 1:17 ` Linus Torvalds
2020-08-18 11:05 ` Christian Brauner
[not found] ` <87pn7m22kn.fsf@x220.int.ebiederm.org>
2020-08-19 15:54 ` Alexei Starovoitov
[not found] ` <871rk0t45v.fsf@x220.int.ebiederm.org>
2020-08-21 16:17 ` Alexei Starovoitov
2020-08-19 18:32 ` Linus Torvalds
2020-08-20 21:50 ` Cyrill Gorcunov
2020-08-17 22:04 ` Eric W. Biederman [this message]
2020-08-18 2:22 ` [PATCH 10/17] proc/fd: In proc_readfd_common use fnext_task Al Viro
[not found] ` <87sgck4o23.fsf@x220.int.ebiederm.org>
2020-08-18 4:59 ` Alexei Starovoitov
2020-08-17 22:04 ` [PATCH 11/17] bpf/task_iter: In task_file_seq_get_next " Eric W. Biederman
2020-08-18 5:39 ` kernel test robot
2020-08-18 12:54 ` Eric W. Biederman
2020-08-17 22:04 ` [PATCH 12/17] proc/fd: In fdinfo seq_show don't use get_files_struct Eric W. Biederman
2020-08-18 0:08 ` Linus Torvalds
[not found] ` <87v9hg69ph.fsf@x220.int.ebiederm.org>
2020-08-18 1:21 ` Linus Torvalds
2020-08-18 10:43 ` Christian Brauner
2020-08-17 22:04 ` [PATCH 13/17] file: Remove get_files_struct Eric W. Biederman
2020-08-18 10:39 ` Christian Brauner
2020-08-17 22:04 ` [PATCH 14/17] file: Merge __fd_install into fd_install Eric W. Biederman
2020-08-18 10:15 ` Christian Brauner
2020-08-17 22:04 ` [PATCH 15/17] file: In f_dupfd read RLIMIT_NOFILE once Eric W. Biederman
2020-08-18 10:12 ` Christian Brauner
2020-08-17 22:04 ` [PATCH 16/17] file: Merge __alloc_fd into alloc_fd Eric W. Biederman
2020-08-18 10:17 ` Christian Brauner
2020-08-17 22:04 ` [PATCH 17/17] file: Rename __close_fd to close_fd and remove the files parameter Eric W. Biederman
2020-08-18 10:19 ` Christian Brauner
2020-08-18 11:20 ` Christoph Hellwig
2020-08-18 12:48 ` Eric W. Biederman
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