Messages in this thread | | | Subject | Re: [PATCH] fs: proc: use down_read_killable in proc_pid_cmdline_read() | From | Yang Shi <> | Date | Wed, 21 Feb 2018 15:13:10 -0800 |
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On 2/21/18 11:57 AM, Alexey Dobriyan wrote: > On Tue, Feb 20, 2018 at 03:38:24PM -0800, Yang Shi wrote: >> >> On 2/20/18 2:38 PM, Alexey Dobriyan wrote: >>> On Wed, Feb 21, 2018 at 03:49:29AM +0800, Yang Shi wrote: >>>> 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. >>>> >>>> down_read_trylock() sounds too aggressive, and we already have killable >>>> version APIs for semaphore, here use down_read_killable() to improve the >>>> responsiveness. >>>> - down_read(&mm->mmap_sem); >>>> + rv = down_read_killable(&mm->mmap_sem); >>>> + if (rv) >>>> + goto out_mmput; >>>> arg_start = mm->arg_start; >>>> arg_end = mm->arg_end; >>>> env_start = mm->env_start; >>> Fix is incomplete >> Yes, it is. Since I just ran into the above splat, so I just did the >> minimum change. >> >>> 1) /proc/*/cmdline only wants to read 4 values atomically, >>> those 4 values are basically random values and aren't >>> related to VM part at all (after C/R went in, they are >>> settable to arbitrary values) >> Sorry, I don't get your point here. Could you please elaborate? > I hoped there is some random spinlock those 4 values could be moved to > but no.
Those 4 values might be changed by prctl_set_mm concurrently if mm->mmap_sem is not acquired.
> >>> 2) access_remote_vm() et al will do the same ->mmap_sem, and >> Yes, it does. But, __access_remote_vm() is called by access_process_vm() >> too, which is used by much more places, i.e. ptrace, so I was not sure >> if it is preferred to convert to killable version. So, I leave it untouched. > Yeah, but ->mmap_sem is taken 3 times per /proc/*/cmdline read > and your scalability tests should trigger next backtrace right away.
Yes, however, I didn't run into it if mmap_sem is acquired earlier.
How about defining a killable version, like __access_remote_vm_killable() which use down_read_killable(), then the killable version can be used by proc/*/cmdline? There might be other users in the future.
Thanks, Yang
> >>> 3) /proc/*/environ and get_cmdline() do the same. >> They look suitable to use killable version. >> >> BTW, I just realized the code should go to out_free_page instead of >> out_mmput. Will rectify in newer version once we decide the extra places >> to use killable version.
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