It's just happened again.
I ran strace on it and it seems like it's in a loop doing this:
futex(0x1184820, FUTEX_WAIT_PRIVATE, 2, NULL) = 0 futex(0x1184820, FUTEX_WAIT_PRIVATE, 2, NULL) = 0 futex(0x1184820, FUTEX_WAIT_PRIVATE, 2, NULL) = 0 futex(0x1184820, FUTEX_WAIT_PRIVATE, 2, NULL) = 0 futex(0x1184820, FUTEX_WAIT_PRIVATE, 2, NULL) = 0 futex(0x1184820, FUTEX_WAIT_PRIVATE, 2, NULL) = 0 etc.
and occasionally I see: futex(0x1184820, FUTEX_WAKE_PRIVATE, 1) = 0
It's just happened again.
I ran strace on it and it seems like it's in a loop doing this:
futex(0x1184820, FUTEX_WAIT_PRIVATE, 2, NULL) = 0
futex(0x1184820, FUTEX_WAIT_PRIVATE, 2, NULL) = 0
futex(0x1184820, FUTEX_WAIT_PRIVATE, 2, NULL) = 0
futex(0x1184820, FUTEX_WAIT_PRIVATE, 2, NULL) = 0
futex(0x1184820, FUTEX_WAIT_PRIVATE, 2, NULL) = 0
futex(0x1184820, FUTEX_WAIT_PRIVATE, 2, NULL) = 0
etc.
and occasionally I see:
futex(0x1184820, FUTEX_WAKE_PRIVATE, 1) = 0