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.
