[src/trunk]: src/sys/kern entropy(9): Nix rnd_trylock_sources.

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/44725368cc64
branches:  trunk
changeset: 364389:44725368cc64
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sun Mar 20 13:44:18 2022 +0000

description:
entropy(9): Nix rnd_trylock_sources.

This was a premature optimization that turned out to be bogus.  It's
not harmful to request more than we need from drivers, so let's not
go out of our way to avoid that.

diffstat:

 sys/kern/kern_entropy.c |  37 ++++++++-----------------------------
 1 files changed, 8 insertions(+), 29 deletions(-)

diffs (68 lines):

diff -r 7ef56e58e545 -r 44725368cc64 sys/kern/kern_entropy.c
--- a/sys/kern/kern_entropy.c   Sun Mar 20 13:18:30 2022 +0000
+++ b/sys/kern/kern_entropy.c   Sun Mar 20 13:44:18 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_entropy.c,v 1.46 2022/03/20 13:18:11 riastradh Exp $      */
+/*     $NetBSD: kern_entropy.c,v 1.47 2022/03/20 13:44:18 riastradh Exp $      */
 
 /*-
  * Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -75,7 +75,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.46 2022/03/20 13:18:11 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.47 2022/03/20 13:44:18 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/types.h>
@@ -1702,30 +1702,10 @@
 }
 
 /*
- * rnd_trylock_sources()
- *
- *     Try to lock the list of sources, but if it's already locked,
- *     fail.  Caller must hold the global entropy lock.  If
- *     successful, no rndsource will go away until rnd_unlock_sources
- *     even while the caller releases the global entropy lock.
- */
-static bool
-rnd_trylock_sources(void)
-{
-
-       KASSERT(E->stage == ENTROPY_COLD || mutex_owned(&E->lock));
-
-       if (E->sourcelock)
-               return false;
-       E->sourcelock = curlwp;
-       return true;
-}
-
-/*
  * rnd_unlock_sources()
  *
- *     Unlock the list of sources after rnd_lock_sources or
- *     rnd_trylock_sources.  Caller must hold the global entropy lock.
+ *     Unlock the list of sources after rnd_lock_sources.  Caller must
+ *     hold the global entropy lock.
  */
 static void
 rnd_unlock_sources(void)
@@ -1768,12 +1748,11 @@
        KASSERT(E->stage == ENTROPY_COLD || mutex_owned(&E->lock));
 
        /*
-        * If there is a request in progress, let it proceed.
-        * Otherwise, note that a request is in progress to avoid
-        * reentry and to block rnd_detach_source until we're done.
+        * Lock the list of entropy sources to block rnd_detach_source
+        * until we're done, and to serialize calls to the entropy
+        * callbacks as guaranteed to drivers.
         */
-       if (!rnd_trylock_sources())
-               return;
+       rnd_lock_sources();
        entropy_request_evcnt.ev_count++;
 
        /* Clamp to the maximum reasonable request.  */