On Tue, 27 Feb 2018 08:25:47 +0800 Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> 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. > Maybe I'm missing something, but I don't see how this solves the problem. Yes, the read of /proc/pid/cmdline will be abandoned if someone interrupts that process. But if nobody does that, the read will still just sit there for 2 minutes and the watchdog warning will still come out? Where the heck are we holding mmap_sem for so long? Can that be fixed? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
