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From: ebiederm@xmission.com (Eric W. Biederman)
To: Arnd Bergmann <arnd@kernel.org>
Cc: Geoff Levand <geoff@infradead.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Oleg Nesterov <oleg@redhat.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH v2 02/24] exec: Simplify unshare_files
Date: Mon, 30 Nov 2020 15:37:45 -0600	[thread overview]
Message-ID: <87o8jeh6fq.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <CAK8P3a0hPG1cTxksTBCJHkAV_=TLZLCi2pZYMk2Dc2-kLzD3rg@mail.gmail.com> (Arnd Bergmann's message of "Fri, 27 Nov 2020 21:29:33 +0100")

Arnd Bergmann <arnd@kernel.org> writes:

> On Wed, Nov 25, 2020 at 2:16 AM Eric W. Biederman <ebiederm@xmission.com> wrote:
>> > On 11/24/20 12:14 PM, Arnd Bergmann wrote:
>> >
>> > There are still PS3-Linux users out there.  They use 'Homebrew' firmware
>> > released through 'Hacker' forums that allow them to run Linux on
>> > non-supported systems.  They are generally hobbies who don't post to
>> > Linux kernel mailing lists.  I get direct inquiries regularly asking
>> > about how to update to a recent kernel.  One of the things that attract
>> > them to the PS3 is the Cell processor and either using or programming
>> > the SPUs.
>> >
>> > It is difficult to judge how much use the SPU core dump support gets,
>> > but if it is not a cause of major problems I feel we should consider
>> > keeping it.
>>
>> I just took a quick look to get a sense how much tool support there is.
>>
>> In the gdb tree I found this 2019 commit abf516c6931a ("Remove Cell
>> Broadband Engine debugging support").  Which basically removes the code
>> in gdb that made sense of the spu coredumps.
>
> Ah, I had not realized this was gone already. The code in gdb for
> seamlessly debugging programs across CPU and SPU was clearly
> more complex than the kernel portion for the coredump, so it makes
> sense this was removed eventually.
>
>> I would not say the coredump support is a source major problems, but it
>> is a challenge to understand.  One of the pieces of code in there that
>> is necessary to make the coredump support work reliable, a call to
>> unshare_files, Oleg whole essentially maintains the ptrace and coredump
>> support did not know why it was there, and it was not at all obvious
>> when I looked at the code.
>>
>> So we are certainly in maintainers loosing hours of time figuring out
>> what is going on and spending time fixing fuzzer bugs related to the
>> code.
>
> I also spent some amount of time on this code earlier this year Christoph
> did some refactoring, and we could both have used that time better.
>
>> At the minimum I will add a few more comments so people reading the code
>> can realize why it is there.   Perhaps putting the relevant code behind
>> a Kconfig so it is only built into the kernel when spufs is present.
>>
>> I think we are at a point we we can start planning on removing the
>> coredump support.  The tools to read it are going away.  None of what is
>> there is bad, but it is definitely a special case, and it definitely has
>> a maintenance cost.
>
> How about adding a comment in the coredump code so it can get
> removed the next time someone comes across it during refactoring,
> or when they find a bug that can't easily be worked around?

Did my proposed patch look ok?

> That way there is still a chance of using it where needed, but
> hopefully it won't waste anyone's time when it gets in the way.

Sounds good to me.

> If there are no objections, I can also send a patch to remove
> CONFIG_PPC_CELL_NATIVE, PPC_IBM_CELL_BLADE and
> everything that depends on those symbols, leaving only the
> bits needed by ps3 in the arch/powerpc/platforms/cell directory.

That also seems reasonable.  My read of the history suggests that
code has been out of commission for a decade or so, and not having it to
trip over (just present in the history) seems very reasonable.

Eric

  reply	other threads:[~2020-11-30 21:39 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 [this message]
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
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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