random: always wake up entropy writers after extraction

Now that POOL_BITS == POOL_MIN_BITS, we must unconditionally wake up
entropy writers after every extraction. Therefore there's no point of
write_wakeup_threshold, so we can move it to the dustbin of unused
compatibility sysctls. While we're at it, we can fix a small comparison
where we were waking up after <= min rather than < min.

Cc: Theodore Ts'o <tytso@mit.edu>
Suggested-by: Eric Biggers <ebiggers@kernel.org>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index d359bcfadd39..d3c6d9a501a9 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -1029,14 +1029,17 @@ This is a directory, with the following entries:
 * ``poolsize``: the entropy pool size, in bits;
 
 * ``urandom_min_reseed_secs``: obsolete (used to determine the minimum
-  number of seconds between urandom pool reseeding).
+  number of seconds between urandom pool reseeding). This file is
+  writable for compatibility purposes, but writing to it has no effect
+  on any RNG behavior.
 
 * ``uuid``: a UUID generated every time this is retrieved (this can
   thus be used to generate UUIDs at will);
 
 * ``write_wakeup_threshold``: when the entropy count drops below this
   (as a number of bits), processes waiting to write to ``/dev/random``
-  are woken up.
+  are woken up. This file is writable for compatibility purposes, but
+  writing to it has no effect on any RNG behavior.
 
 If ``drivers/char/random.c`` is built with ``ADD_INTERRUPT_BENCH``
 defined, these additional entries are present: