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From: Al Viro <viro@zeniv.linux.org.uk>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	criu@openvz.org, bpf@vger.kernel.org,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	"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>
Subject: Re: [PATCH 10/17] proc/fd: In proc_readfd_common use fnext_task
Date: Tue, 18 Aug 2020 03:22:49 +0100	[thread overview]
Message-ID: <20200818022249.GC1236603@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200817220425.9389-10-ebiederm@xmission.com>

On Mon, Aug 17, 2020 at 05:04:18PM -0500, Eric W. Biederman wrote:
> 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.

Yecchhh...  So you keep locking/unlocking the damn thing for each
descriptor?

  reply	other threads:[~2020-08-18  2:23 UTC|newest]

Thread overview: 48+ 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 ` [PATCH 10/17] proc/fd: In proc_readfd_common use fnext_task Eric W. Biederman
2020-08-18  2:22   ` Al Viro [this message]
     [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  5:39     ` kernel test robot
2020-08-18 12:54     ` Eric W. Biederman
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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