linux-kernel - [PATCH 09/11] random: forget lock in lockless accounting

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Message-ID: <20131107235926.GL16018@ringworld.MIT.EDU>
Date:	Thu, 7 Nov 2013 18:59:26 -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 09/11] 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 | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 9e4645e..1bf6bf8 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -843,9 +843,6 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min,
 	unsigned long flags;
 	int wakeup_write = 0;
 
-	/* Hold lock while accounting */
-	spin_lock_irqsave(&r->lock, flags);
-
 	BUG_ON(r->entropy_count > r->poolinfo->POOLBITS);
 	DEBUG_ENT("trying to extract %zu bits from %s\n",
 		  nbytes * 8, r->name);
@@ -871,8 +868,6 @@ retry:
 	DEBUG_ENT("debiting %zu entropy credits from %s%s\n",
 		  nbytes * 8, r->name, r->limit ? "" : " (unlimited)");
 
-	spin_unlock_irqrestore(&r->lock, flags);
-
 	if (wakeup_write) {
 		wake_up_interruptible(&random_write_wait);
 		kill_fasync(&fasync, SIGIO, POLL_OUT);
-- 
1.8.3.2

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