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@xxxxxxxxxxxxxxxxx> > Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > --- > 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(-)
