From: "Paul E. McKenney" <paulmck@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Christian Brauner <christian.brauner@ubuntu.com>,
Oleg Nesterov <oleg@redhat.com>, Jann Horn <jann@thejh.net>
Subject: Re: [PATCH] files: rcu free files_struct
Date: Wed, 9 Dec 2020 15:26:18 -0800 [thread overview]
Message-ID: <20201209232618.GK2657@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20201209230755.GV7338@casper.infradead.org>
On Wed, Dec 09, 2020 at 11:07:55PM +0000, Matthew Wilcox wrote:
> On Wed, Dec 09, 2020 at 03:01:36PM -0800, Linus Torvalds wrote:
> > On Wed, Dec 9, 2020 at 2:58 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
> > >
> > > On Wed, Dec 09, 2020 at 07:49:38PM +0000, Matthew Wilcox wrote:
> > > >
> > > > Assuming this is safe, you can use RCU_INIT_POINTER() here because you're
> > > > storing NULL, so you don't need the wmb() before storing the pointer.
> > >
> > > fs/file.c:pick_file() would make more interesting target for the same treatment...
> >
> > Actually, don't.
> >
> > rcu_assign_pointer() itself already does the optimization for the case
> > of a constant NULL pointer assignment.
> >
> > So there's no need to manually change things to RCU_INIT_POINTER().
>
> I missed that, and the documentation wasn't updated by
> 3a37f7275cda5ad25c1fe9be8f20c76c60d175fa.
Can't trust the author of that patch! ;-)
> Paul, how about this?
>
> +++ b/Documentation/RCU/Design/Requirements/Requirements.rst
> @@ -1668,8 +1668,10 @@ against mishaps and misuse:
> this purpose.
> #. It is not necessary to use rcu_assign_pointer() when creating
> linked structures that are to be published via a single external
> - pointer. The RCU_INIT_POINTER() macro is provided for this task
> - and also for assigning ``NULL`` pointers at runtime.
> + pointer. The RCU_INIT_POINTER() macro is provided for this task.
> + It used to be more efficient to use RCU_INIT_POINTER() to store a
> + ``NULL`` pointer, but rcu_assign_pointer() now optimises for a constant
> + ``NULL`` pointer itself.
>
> This not a hard-and-fast list: RCU's diagnostic capabilities will
> continue to be guided by the number and type of usage bugs found in
Looks good to me! If you send a complete patch, I will be happy to pull
it in.
Thanx, Paul
next prev parent reply other threads:[~2020-12-09 23:27 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 ` [PATCH v2 15/24] proc/fd: In proc_readfd_common use task_lookup_next_fd_rcu Eric W. Biederman
2020-12-07 23:29 ` 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 [this message]
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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