In man/man7/signal.7 it says:

If a blocked call to one of the following interfaces is interrupted
by a signal handler, then the call is automatically restarted after
the signal handler returns if the SA_RESTART flag was used;
otherwise the call fails with the error EINTR:
(...)
• pthread_mutex_lock(3), pthread_cond_wait(3), and related APIs.

I don't understand this, in my experiments neither
pthread_mutex_lock() nor pthread_cond_wait() return EINTR even if
signal handler was installed without using SA_RESTART flag. The
underlying futex() call indeed fails with EINTR but it's called again
by both glibc and musl. Additionally both
man/man3/pthread_mutex_lock.3 and man/man3/pthread_cond_wait.3 say
that these functions do not return EINTR.

Is my understanding of the signal.7 wrong or does it need some work?

-- 
Arkadiusz Drabczyk [off-list ref]