Hi All, A quick question: If any of user space process is hanged or not responding, does it means kernel is also hung in some part? I trying to understand why hang happens and what triggers it.happening ? How to go about recover a hang process, apart from restarting it. Regards, Vipul.
Usually a user process can hang inside kernel if it makes a system call and is blocked inside kernel waiting on a semaphore (where it would leave CPU) or spinning for a spinlock which might lock down the CPU core. You can examine where process is stuck by: # echo w > /proc/sysrq-trigger This sysrq will show you hung tasks and their stack trace in /var/log/messages or dmesg output. But a process might as well hang in user mode e.g. on user mode semaphore. Most of the time there are some logical bugs in the program or kernel subsystems for which hang occurs which needs to be fixed instead of just restarting the process. Might work for user mode hang, but may not for hang inside kernel. Rajat On Thu, Dec 5, 2013 at 8:34 PM, Vipul Jain <vipulsj@gmail.com> wrote:
Hi All,
A quick question:
If any of user space process is hanged or not responding, does it means kernel is also hung in some part? I trying to understand why hang happens and what triggers it.happening ? How to go about recover a hang process, apart from restarting it.
Regards, Vipul.
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Hi Vipul, Although you havent provided any technical info regarding your hand issue But anyways I would sugegst you to perform very basic debugging techniques: 1) raise the kernel log level to highest "echo 8 > /proc/sys/kernel/printk" 2) try to reproduce it and narrowdown your issue to a perticular scenario at which this hang happens or it happens randomly. 3) Then try to log inside user code that is responsible in that perticular scenario and then post your exact execution code point of problem. Otherwise it is hard to say where the issue lies and it will just be bluffing nothing else. Regards Sanjay On Fri, Dec 6, 2013 at 10:04 AM, Vipul Jain <vipulsj@gmail.com> wrote:
Hi All,
A quick question:
If any of user space process is hanged or not responding, does it means kernel is also hung in some part? I trying to understand why hang happens and what triggers it.happening ? How to go about recover a hang process, apart from restarting it.
Regards, Vipul.
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Rajat Sharma -
Sanjay Das -
Vipul Jain