From: Andrew Morton <akpm@linux-foundation.org>
To: Yang Shi <yang.shi@linux.alibaba.com>
Cc: adobriyan@gmail.com, mhocko@kernel.org, willy@infradead.org,
mguzik@redhat.com, gorcunov@gmail.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [v4 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct
Date: Tue, 17 Apr 2018 11:29:57 -0700 [thread overview]
Message-ID: <20180417112957.84de526138f404a04298ec4c@linux-foundation.org> (raw)
In-Reply-To: <1523730291-109696-1-git-send-email-yang.shi@linux.alibaba.com>
On Sun, 15 Apr 2018 02:24:51 +0800 Yang Shi <yang.shi@linux.alibaba.com> wrote:
> mmap_sem is on the hot path of kernel, and it very contended, but it is
> abused too. It is used to protect arg_start|end and evn_start|end when
> reading /proc/$PID/cmdline and /proc/$PID/environ, but it doesn't make
> sense since those proc files just expect to read 4 values atomically and
> not related to VM, they could be set to arbitrary values by C/R.
>
> And, the mmap_sem contention may cause unexpected issue like below:
>
> INFO: task ps:14018 blocked for more than 120 seconds.
> Tainted: G E 4.9.79-009.ali3000.alios7.x86_64 #1
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
> message.
> ps D 0 14018 1 0x00000004
> ffff885582f84000 ffff885e8682f000 ffff880972943000 ffff885ebf499bc0
> ffff8828ee120000 ffffc900349bfca8 ffffffff817154d0 0000000000000040
> 00ffffff812f872a ffff885ebf499bc0 024000d000948300 ffff880972943000
> Call Trace:
> [<ffffffff817154d0>] ? __schedule+0x250/0x730
> [<ffffffff817159e6>] schedule+0x36/0x80
> [<ffffffff81718560>] rwsem_down_read_failed+0xf0/0x150
> [<ffffffff81390a28>] call_rwsem_down_read_failed+0x18/0x30
> [<ffffffff81717db0>] down_read+0x20/0x40
> [<ffffffff812b9439>] proc_pid_cmdline_read+0xd9/0x4e0
> [<ffffffff81253c95>] ? do_filp_open+0xa5/0x100
> [<ffffffff81241d87>] __vfs_read+0x37/0x150
> [<ffffffff812f824b>] ? security_file_permission+0x9b/0xc0
> [<ffffffff81242266>] vfs_read+0x96/0x130
> [<ffffffff812437b5>] SyS_read+0x55/0xc0
> [<ffffffff8171a6da>] entry_SYSCALL_64_fastpath+0x1a/0xc5
>
> Both Alexey Dobriyan and Michal Hocko suggested to use dedicated lock
> for them to mitigate the abuse of mmap_sem.
>
> So, introduce a new spinlock in mm_struct to protect the concurrent
> access to arg_start|end, env_start|end and others, as well as replace
> write map_sem to read to protect the race condition between prctl and
> sys_brk which might break check_data_rlimit(), and makes prctl more
> friendly to other VM operations.
(We should move check_data_rlimit() out of the .h file)
It seems inconsistent to be using mmap_sem to protect ->start_brk and
friends in sys_brk(). We've already declared that these are protected
by arg_lock so that's what we should be using? And getting this
consistent should permit us to stop using mmap_sem in prctl()
altogether?
next prev parent reply other threads:[~2018-04-17 18:30 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-14 18:24 [v4 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct Yang Shi
2018-04-15 20:49 ` Cyrill Gorcunov
2018-04-17 18:29 ` Andrew Morton [this message]
2018-04-17 20:39 ` Cyrill Gorcunov
2018-04-18 8:00 ` Michal Hocko
2018-04-17 20:52 ` Yang Shi
2018-04-18 8:05 ` Michal Hocko
2018-04-18 9:02 ` Cyrill Gorcunov
2018-04-18 9:03 ` Michal Hocko
2018-04-18 9:40 ` Cyrill Gorcunov
2018-04-18 18:18 ` Yang Shi
2018-04-18 10:11 ` Kirill Tkhai
2018-04-18 18:48 ` Yang Shi
2018-04-18 22:59 ` Kirill Tkhai
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180417112957.84de526138f404a04298ec4c@linux-foundation.org \
--to=akpm@linux-foundation.org \
--cc=adobriyan@gmail.com \
--cc=gorcunov@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mguzik@redhat.com \
--cc=mhocko@kernel.org \
--cc=willy@infradead.org \
--cc=yang.shi@linux.alibaba.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).