ABOUT hung_task_timeout_secs
if a task(process) is hung then hung_task_timeout_secs value
decides if the hung task needs no reboot or reboot after
n seconds
LINUX KERNEL RELATED PARAMETER
$cat /proc/sys/kernel/hung_task_timeout_secs
120
$
$echo 0 | sudo tee –append /proc/sys/kernel/ hung_task_timeout_secs
0
$sudo cat /proc/sys/kernel/hung_task_timeout_secs
0
$
When a task in D state did not get scheduled for more than
this value report a warning.This file shows up if CONFIG_
DETECT_HUNG_TASK is enabled.
0: means infinite timeout - no checking done. Possible values
to set are in range {0..LONG_MAX/HZ}.
PARAMETER RELATED
TEST-MAIL1 ~ #dmesg
“echo 0 > /proc/sys/kernel/hung_task_timeout_secs” disables this message.
rm D ffff88107f472c40 0 16705 22512 0x00000000
ffff881014693810 0000000000000086 ffff881000000000 ffff88102013b040
0000000000012c40 ffff880471855fd8 0000000000012c40 ffff880471854010
ffff880471855fd8 0000000000012c40 ffff881017ff8e40 0000000100000000
Call Trace:
[<ffffffff8148d45d>] ? schedule_timeout+0x1ed/0x2d0
[<ffffffffa0b7d1ea>] ? dlmlock+0x8a/0xda0 [ocfs2_dlm]
[<ffffffff8148ce5c>] ? wait_for_common+0x12c/0x1a0
[<ffffffff81052230>] ? try_to_wake_up+0x280/0x280
[<ffffffffa0a3b9c0>] ? __ocfs2_cluster_lock+0x1f0/0x780 [ocfs2]
[<ffffffff8148ce80>] ? wait_for_common+0x150/0x1a0
[<ffffffffa0a9c6bc>] ? ocfs2_buffer_cached+0x8c/0x180 [ocfs2]
[<ffffffffa0a40bc6>] ? ocfs2_inode_lock_full_nested+0x126/0x540 [ocfs2]
[<ffffffffa0a5922e>] ? ocfs2_lookup_lock_orphan_dir+0x6e/0x1b0 [ocfs2]
[<ffffffffa0a5922e>] ? ocfs2_lookup_lock_orphan_dir+0x6e/0x1b0 [ocfs2]
[<ffffffffa0a5ba1a>] ? ocfs2_prepare_orphan_dir+0x4a/0x290 [ocfs2]
[<ffffffffa0a5e621>] ? ocfs2_unlink+0x6e1/0xbb0 [ocfs2]
[<ffffffff811bcfea>] ? may_link+0xda/0x170
[<ffffffff81141c8e>] ? vfs_unlink+0x9e/0x100
[<ffffffff81145881>] ? do_unlinkat+0x1a1/0x1d0
[<ffffffff81147b00>] ? vfs_readdir+0xa0/0xe0
[<ffffffff8116fedb>] ? fsnotify_find_inode_mark+0x2b/0x40
[<ffffffff81170c24>] ? dnotify_flush+0x54/0x110
[<ffffffff81133eec>] ? filp_close+0x5c/0x90
[<ffffffff81496912>] ? system_call_fastpath+0x16/0x1b
CLASSROOM
While waiting for read() or write() to/from a file
descriptor return, the process will be put in aspecial
kind of sleep, known as "D" or "Disk Sleep". This is
special, because the process can not be killed or
interrupted while in such a state. A process waiting
for a return from ioctl()
would also be put to sleep in this manner.
RELATED SOURCE CODE EXPOSURE
/*
* Ok, the task did not get scheduled for more than 2 minutes,
* complain:
*/
if (sysctl_hung_task_warnings) {
if (sysctl_hung_task_warnings > 0)
sysctl_hung_task_warnings–;
pr_err(“INFO: task %s:%d blocked for more than %ld seconds.\n”,
t->comm, t->pid, timeout);
pr_err(” %s %s %.*s%s\n”,
print_tainted(), init_utsname()->release,
(int)strcspn(init_utsname()->version, ” “),
init_utsname()->version,
LINUX_PACKAGE_ID);
pr_err(“\”echo 0 > /proc/sys/kernel/hung_task_timeout_secs\””
” disables this message.\n”);
sched_show_task(t);
hung_task_show_lock = true;
}
[/c]
[c light=”true”]
/*
* Process updating of timeout sysctl
*/
int proc_dohung_task_timeout_secs(struct ctl_table * styletable, int write,
void __user *buffer,
size_t *lenp, loff_t *ppos)
{
int ret;
ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
if (ret || !write)
goto out;
wake_up_process(watchdog_task);
out:
return ret;
}
[/c]
SOURCE CODE TAKEN FROM OFFICIAL LINUX KERNEL
RELATED FROM RESEARCH PAPER
Kernel data collection tools. Several monitoring facilities are
provided by the Linux kernel, which have been exploited in this
work. In particular, we use KProbes which inserts breakpoints in
arbitrary binary code locations in charge of triggering user-defined
handler functions. Handlers can be used to collect information
about internal kernel variables; subsequently, kernel execution is
restored. Kdump is a tool for failure data collection based on the
execution of a secondary kernel, namely capture kernel, which is
preliminarily loaded into a reserved memory region. When the
primary kernel fails, the capture kernel is executed; then, it can
collect failure data by reading the main memory state. Built-in
hang detection mechanisms. Several hang detection mechanisms are
available in the Linux OS, which can be enabled by recompiling the
kernel. In particular, the following facilities can be used for
hang detection: Soft lockup detection, i.e., the kernel detects
whether a "canary" task is not scheduled within a timeout; Hard
lockup detection, i.e., if any CPU in the system does not handles
local timer interrupt for longer than a timeout;
Sleep-inside-spinlock checking, i.e., assertions that verify
whether there are spinlocks that have been acquired before calling
a sleeping function (i.e., a function during which the current
thread may block and be preempted by the scheduler); Checks on lock
API usage, that is: missing lock initialization, release of an
already freed lock, release of a lock by a thread or CPU different
from the lock holder, lock data structure corruption.
source : http://tinyurl.com/7pt5j9a
Assessment and Improvement of Hang Detection in the Linux Operating System
2009 28th IEEE International Symposium on Reliable Distributed System
LINKS
https://access.redhat.com/solutions/60572
https://www.linuxquestions.org/questions/linux-software-2/kernel-panic-echo-0-proc-sys-kernel-4175629199/
https://www.kernel.org/doc/Documentation/sysctl/kernel.txt
https://stackoverflow.com/questions/84882/sudo-echo-something-etc-privilegedfile-doesnt-work-is-there-an-alterna
https://www.tldp.org/LDP/tlk/kernel/processes.html
https://www.nico.schottelius.org/blog/reboot-linux-if-task-blocked-for-more-than-n-seconds/
http://stackoverflow.com/questions/1475683/linux-process-states