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Subject[PATCH] fs: proc: use down_read_killable in proc_pid_cmdline_read()
Date
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.

Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
---
fs/proc/base.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9298324..44b6f8f 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -242,7 +242,9 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
goto out_mmput;
}

- 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;
--
1.8.3.1
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