On Tue, 27 Feb 2018, Yang Shi wrote: > > Background: > When running vm-scalability with large memory (> 300GB), the below hung > task issue happens occasionally. > > 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 > > When manipulating a large mapping, the process may hold the mmap_sem for > long time, so reading /proc/<pid>/cmdline may be blocked in > uninterruptible state for long time. > We already have killable version APIs for semaphore, here use > down_read_killable() > to improve the responsiveness. >
Rather than killable, we have patches that introduce down_read_unfair() variants for the files you've modified (cmdline and environ) as well as others (maps, numa_maps, smaps). When another thread is holding down_read() and there are queued down_write()'s, down_read_unfair() allows for grabbing the rwsem without queueing for it. Additionally, when another thread is holding down_write(), down_read_unfair() allows for queueing in front of other threads trying to grab it for write as well. Ingo would know more about whether a variant like that in upstream Linux would be acceptable. Would you be interested in unfair variants instead of only addressing killable?
