linux-kernel - Re: [PATCH 4/7] random: remove unused reserved argument

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Message-ID: <YeRGSPTpJlSTJdgO@zx2c4.com>
Date:   Sun, 16 Jan 2022 17:22:32 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Dominik Brodowski <linux@...inikbrodowski.net>
Cc:     linux-kernel@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH 4/7] random: remove unused reserved argument

On Sun, Jan 16, 2022 at 2:45 PM Dominik Brodowski <linux@...inikbrodowski.net> wrote:
> > @@ -1342,7 +1341,7 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min,
> >       /* never pull more than available */
> >       have_bytes = entropy_count >> (ENTROPY_SHIFT + 3);
> > 
> > -     if ((have_bytes -= reserved) < 0)
> > +     if (have_bytes < 0)
> >               have_bytes = 0;
> >       ibytes = min_t(size_t, ibytes, have_bytes);
>
> Hmm. We already WARN_ON(entropy_count < 0) a few lines below. Maybe move
> that assertion before the assignement of have_bytes? Then, have_bytes can
> never be lower than zero, and the code becomes even simpler. What do you
> think?

Can you send a separate patch for this that we can apply on top? It
seems reasonable anyhow. Something like:

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 327086b35797..419156d2146d 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1329,7 +1329,7 @@ EXPORT_SYMBOL_GPL(add_disk_randomness);
  */
 static size_t account(struct entropy_store *r, size_t nbytes, int min)
 {
-	int entropy_count, orig, have_bytes;
+	int entropy_count, orig;
 	size_t ibytes, nfrac;

 	BUG_ON(r->entropy_count > POOL_FRACBITS);
@@ -1337,21 +1337,17 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min)
 	/* Can we pull enough? */
 retry:
 	entropy_count = orig = READ_ONCE(r->entropy_count);
-	ibytes = nbytes;
-	/* never pull more than available */
-	have_bytes = entropy_count >> (ENTROPY_SHIFT + 3);
-
-	if (have_bytes < 0)
-		have_bytes = 0;
-	ibytes = min_t(size_t, ibytes, have_bytes);
-	if (ibytes < min)
-		ibytes = 0;
-
 	if (WARN_ON(entropy_count < 0)) {
 		pr_warn("negative entropy count: pool %s count %d\n",
 			r->name, entropy_count);
 		entropy_count = 0;
 	}
+
+	/* never pull more than available */
+	ibytes = min_t(size_t, nbytes, entropy_count >> (ENTROPY_SHIFT + 3));
+	if (ibytes < min)
+		ibytes = 0;
+
 	nfrac = ibytes << (ENTROPY_SHIFT + 3);
 	if ((size_t) entropy_count > nfrac)
 		entropy_count -= nfrac;