When does thread get into uncancellable sleep state - linux

Question

I have this piece of code where it works perfects in normal case. however , sometimes thread get into uncancelable sleep state.
It means from the state of the process, I see this thread getting into this https://code.woboq.org/userspace/glibc/sysdeps/unix/sysv/linux/nanosleep_nocancel.c.html#__nanosleep_nocancel
struct timespec convertticktotimespec(unsigned long numticks)
{
struct timespec tm;
/* separate the integer and decimal portions */
long nanoseconds =
((numticks / (float)sysconf(_SC_CLK_TCK)) - floor(numticks / (float)sysconf(_SC_CLK_TCK))) *
NANOSEC_MULTIPLIER;
tm.tv_sec = numticks / sysconf(_SC_CLK_TCK);
tm.tv_nsec = nanoseconds;
return tm;
}
void *thread(void *args)
{
struct_S *s = (struct_S *)args;
while(1)
{
s->var = 1;
struct timespec tm = convertticktotimespec(sysClkRateGet() * 13);
if ( 0 !=nanosleep(&tm, NULL) ) {
perror(nanosleep);
}
}
}
stack trace looks like this
Thread 19 (Thread 0x7f225a043700 (LWP 16023)):
#0 0x00007f225b8913ed in __accept_nocancel () at ../sysdeps/unix/syscall-
template.S:84
#1 0x0000000000000000 in ?? ()
Thread 18 (Thread 0x7f225a076700 (LWP 15952)):
#0 0x00007f225b89126d in __close_nocancel () at ../sysdeps/unix/syscall-template.S:84
#1 0x0000000000000000 in ?? ()
Thread 14 (Thread 0x7f225a021700 (LWP 16035)):
#0 0x00007f225b8917dd in __nanosleep_nocancel () at ../sysdeps/unix/syscall-template.S:84
#1 0x0000000000000000 in ?? ()
Thread 13 (Thread 0x7f225a032700 (LWP 16034)):
#0 0x00007f225b8917dd in __nanosleep_nocancel () at ../sysdeps/unix/syscall-template.S:84
#1 0x0000000000000000 in ?? ()
Thread 3 (Thread 0x7f225bbb3700 (LWP 15950)):
#0 0x00007f225ab1e3f3 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#1 0x0000000000000000 in ?? ()
Thread 2 (Thread 0x7f225a010700 (LWP 16036)):
#0 0x00007f225b8911ad in __write_nocancel () at ../sysdeps/unix/syscall-template.S:84
#1 0x0000000000000000 in ?? ()
some how this thread getting into uncancelable sleep state on random , although I dont find the clear definition of this anywhere on internet, so I assume thread getting sleep state forever which can not be interrupted .hence this thread goes to inactive state forever.
I have no clue why is this happening having executing or responsible for fewer lines of code or instructions.
fromcode.woboq , I found that this gets called from mutex lock.
https://code.woboq.org/userspace/glibc nptl/pthread_mutex_timedlock.c.html#416, but the thread is not using any mutex.
the only thing that i suspect here is , structure struct_s is allocated in the shared memory. this variable is also accessed and assigned by other thread from an another process. does the thread get into this state , internally depending on priority of the threads ?