lkml.org 
[lkml]   [2018]   [Mar]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct
From
Date
On 2018/03/24 9:36, Yang Shi wrote:
> 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

Yes, but

>
> Both Alexey Dobriyan and Michal Hocko suggested to use dedicated lock
> for them to mitigate the abuse of mmap_sem.
>
> So, introduce a new rwlock in mm_struct to protect the concurrent access
> to arg_start|end and env_start|end.

does arg_lock really help?

I wonder whether per "struct mm_struct" granularity is needed if arg_lock
protects only a few atomic reads. A global lock would be sufficient.

Also, even if we succeeded to avoid mmap_sem contention at that location,
won't we after all get mmap_sem contention messages a bit later, for
access_remote_vm() holds mmap_sem which would lead to traces like above
if mmap_sem is already contended?

>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> Cc: Alexey Dobriyan <adobriyan@gmail.com>
> Cc: Michal Hocko <mhocko@kernel.org>
> ---
> fs/proc/base.c | 8 ++++----
> include/linux/mm_types.h | 2 ++
> kernel/fork.c | 1 +
> kernel/sys.c | 6 ++++++
> mm/init-mm.c | 1 +
> 5 files changed, 14 insertions(+), 4 deletions(-)

\
 
 \ /
  Last update: 2018-03-26 16:50    [W:0.078 / U:20.260 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site