Messages in this thread | | | Subject | Re: [PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct | From | Yang Shi <> | Date | Mon, 26 Mar 2018 11:31:03 -0400 |
| |
On 3/26/18 10:49 AM, Tetsuo Handa wrote: > 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.
However, a global lock might be hard to know what it is used for, and might be abused again.
And, it may introduce unexpected contention for parallel reading for /proc
> > 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?
Yes, definitely, this patch is aimed to remove the abuse to mmap_sem. The mmap_sem contention will be addressed separately.
Yang
> >> 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(-)
| |