I have written a (free OSS) Linux tool called `psn` for this kind of stuff [1]. It samples each interesting thread's state from /proc/PID/task/TID/status,wchan,syscall etc and shows you a summary of which threads were blocked in which state, in which syscalls and where in the kernel were they stuck (wchan). It can be used with applications like pv, tar, dd, mysqld, httpd, etc.

[1] https://0x.tools/#linux-process-snapper