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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@infradead.org>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	"Trond Myklebust" <trond.myklebust@hammerspace.com>,
	"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>,
	"Andy Lavr" <andy.lavr@gmail.com>
Subject: [PATCH v2 15/24] proc/fd: In proc_readfd_common use task_lookup_next_fd_rcu
Date: Fri, 20 Nov 2020 17:14:32 -0600	[thread overview]
Message-ID: <20201120231441.29911-15-ebiederm@xmission.com> (raw)
In-Reply-To: <87r1on1v62.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 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
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 c1a984f3c4df..72c1525b4b3e 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;
-- 
2.25.0


  parent reply	other threads:[~2020-11-20 23:20 UTC|newest]

Thread overview: 77+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <87r1on1v62.fsf@x220.int.ebiederm.org>
2020-11-20 23:14 ` [PATCH v2 01/24] exec: Move unshare_files to fix posix file locking during exec Eric W. Biederman
2020-11-20 23:58   ` Linus Torvalds
2020-12-07 22:22   ` Al Viro
     [not found]     ` <87zh2pusdw.fsf@x220.int.ebiederm.org>
2020-12-07 23:35       ` Al Viro
2020-11-20 23:14 ` [PATCH v2 02/24] exec: Simplify unshare_files Eric W. Biederman
2020-11-23 17:50   ` Oleg Nesterov
2020-11-23 18:25     ` Linus Torvalds
     [not found]       ` <87im9vx08i.fsf@x220.int.ebiederm.org>
     [not found]         ` <87pn42r0n7.fsf@x220.int.ebiederm.org>
2020-11-24 19:58           ` Linus Torvalds
2020-11-24 20:14             ` Arnd Bergmann
2020-11-24 23:44               ` Geoff Levand
2020-11-25  1:16                 ` Eric W. Biederman
2020-11-27 20:29                   ` Arnd Bergmann
2020-11-30 21:37                     ` Eric W. Biederman
2020-12-01  9:46                     ` Michael Ellerman
2020-11-25 21:51                 ` [RFC][PATCH] coredump: Document coredump code exclusively used by cell spufs Eric W. Biederman
2020-12-02 15:20                   ` Eric W. Biederman
2020-12-02 15:58                     ` Arnd Bergmann
2020-12-07 22:32       ` [PATCH v2 02/24] exec: Simplify unshare_files Al Viro
2020-11-20 23:14 ` [PATCH v2 03/24] exec: Remove reset_files_struct Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 04/24] kcmp: In kcmp_epoll_target use fget_task Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 05/24] bpf: In bpf_task_fd_query " Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 06/24] proc/fd: In proc_fd_link " Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 07/24] file: Rename __fcheck_files to files_lookup_fd_raw Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 08/24] file: Factor files_lookup_fd_locked out of fcheck_files Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 09/24] file: Replace fcheck_files with files_lookup_fd_rcu Eric W. Biederman
2020-12-07 22:46   ` Al Viro
2020-12-07 22:49     ` Al Viro
2020-12-09 16:54       ` Al Viro
2020-12-09 17:44         ` Paul E. McKenney
2020-11-20 23:14 ` [PATCH v2 10/24] file: Rename fcheck lookup_fd_rcu Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 11/24] file: Implement task_lookup_fd_rcu Eric W. Biederman
2020-11-21 18:19   ` Cyrill Gorcunov
     [not found]     ` <87blfp1r8b.fsf@x220.int.ebiederm.org>
2020-11-22 13:52       ` Cyrill Gorcunov
2020-11-20 23:14 ` [PATCH v2 12/24] proc/fd: In tid_fd_mode use task_lookup_fd_rcu Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 13/24] kcmp: In get_file_raw_ptr " Eric W. Biederman
2020-11-23 21:05   ` Cyrill Gorcunov
2020-11-20 23:14 ` [PATCH v2 14/24] file: Implement task_lookup_next_fd_rcu Eric W. Biederman
2020-11-20 23:14 ` Eric W. Biederman [this message]
2020-12-07 23:29   ` [PATCH v2 15/24] proc/fd: In proc_readfd_common use task_lookup_next_fd_rcu Al Viro
     [not found]     ` <877dprvs8e.fsf@x220.int.ebiederm.org>
2020-12-09  4:07       ` Al Viro
     [not found]         ` <877dprtxly.fsf@x220.int.ebiederm.org>
2020-12-09 14:23           ` Al Viro
2020-12-09 18:04             ` [PATCH] files: rcu free files_struct Eric W. Biederman
2020-12-09 19:13               ` Linus Torvalds
2020-12-09 19:50                 ` Al Viro
2020-12-09 21:32                   ` Eric W. Biederman
2020-12-10  6:13                     ` Al Viro
2020-12-10 19:29                       ` Eric W. Biederman
2020-12-10 21:36                         ` Al Viro
2020-12-10 22:30                           ` Christian Brauner
2020-12-10 22:54                             ` Al Viro
2020-12-10 23:10                               ` Al Viro
2020-12-09 21:42                   ` [PATCH -1/24] exec: Don't open code get_close_on_exec Eric W. Biederman
2020-12-09 22:04                 ` [PATCH] files: rcu free files_struct Eric W. Biederman
2020-12-09 19:49               ` Matthew Wilcox
2020-12-09 22:06                 ` Eric W. Biederman
2020-12-09 22:58                 ` Al Viro
2020-12-09 23:01                   ` Linus Torvalds
2020-12-09 23:04                     ` Linus Torvalds
2020-12-09 23:07                     ` Matthew Wilcox
2020-12-09 23:26                       ` Paul E. McKenney
2020-12-09 23:29                       ` Linus Torvalds
2020-12-10  0:39                         ` Paul E. McKenney
2020-12-10  0:41                           ` Linus Torvalds
2020-12-10  0:57                             ` Paul E. McKenney
2020-11-20 23:14 ` [PATCH v2 16/24] bpf/task_iter: In task_file_seq_get_next use task_lookup_next_fd_rcu Eric W. Biederman
2020-11-23 17:06   ` Yonghong Song
2020-11-20 23:14 ` [PATCH v2 17/24] proc/fd: In fdinfo seq_show don't use get_files_struct Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 18/24] file: Merge __fd_install into fd_install Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 19/24] file: In f_dupfd read RLIMIT_NOFILE once Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 20/24] file: Merge __alloc_fd into alloc_fd Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 21/24] file: Rename __close_fd to close_fd and remove the files parameter Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 22/24] file: Replace ksys_close with close_fd Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 23/24] file: Rename __close_fd_get_file close_fd_get_file Eric W. Biederman
2020-11-20 23:14 ` [PATCH v2 24/24] file: Remove get_files_struct Eric W. Biederman
2020-11-21  0:05 ` [PATCH v2 00/24] exec: Move unshare_files and guarantee files_struct.count is correct Linus Torvalds
2020-11-28  5:12   ` Al Viro
2020-12-07 23:56     ` Al Viro

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