linux-kernel - [PATCH 7/9] random: forget lock in lockless accounting

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Message-ID: <20131113080828.GU16018@ringworld.MIT.EDU>
Date:	Wed, 13 Nov 2013 03:08:28 -0500
From:	Greg Price <price@....EDU>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	linux-kernel@...r.kernel.org, Jiri Kosina <jkosina@...e.cz>
Subject: [PATCH 7/9] random: forget lock in lockless accounting

The only mutable data accessed here is ->entropy_count, but since
902c098a3 ("random: use lockless techniques in the interrupt path")
that member isn't protected by the lock anyway.  Since 10b3a32d2
("random: fix accounting race condition") we use cmpxchg to protect
our accesses to ->entropy_count here.  Drop the use of the lock.

Cc: Jiri Kosina <jkosina@...e.cz>
Cc: "Theodore Ts'o" <tytso@....edu>
Signed-off-by: Greg Price <price@....edu>
---
 drivers/char/random.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 5dffca8..1f43f9e 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -974,9 +974,6 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min,
 	int entropy_count, orig;
 	size_t ibytes;
 
-	/* Hold lock while accounting */
-	spin_lock_irqsave(&r->lock, flags);
-
 	BUG_ON(r->entropy_count > r->poolinfo->poolfracbits);
 
 	/* Can we pull enough? */
@@ -999,7 +996,6 @@ retry:
 		    < random_write_wakeup_thresh)
 			wakeup_write = 1;
 	}
-	spin_unlock_irqrestore(&r->lock, flags);
 
 	trace_debit_entropy(r->name, 8 * ibytes);
 	if (wakeup_write) {
-- 
1.8.3.2

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