This is a note to let you know that I've just added the patch titled
random: use lockless method of accessing and updating f->reg_idx
to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
random-use-lockless-method-of-accessing-and-updating-f-reg_idx.patch
and it can be found in the queue-3.18 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 92e75428ffc90e2a0321062379f883f3671cfebe Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@xxxxxxx>
Date: Wed, 7 Jun 2017 19:01:32 -0400
Subject: random: use lockless method of accessing and updating f->reg_idx
From: Theodore Ts'o <tytso@xxxxxxx>
commit 92e75428ffc90e2a0321062379f883f3671cfebe upstream.
Linus pointed out that there is a much more efficient way of avoiding
the problem that we were trying to address in commit 9dfa7bba35ac0:
"fix race in drivers/char/random.c:get_reg()".
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Cc: Michael Schmitz <schmitzmic@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/char/random.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -863,15 +863,15 @@ static void add_interrupt_bench(cycles_t
static __u32 get_reg(struct fast_pool *f, struct pt_regs *regs)
{
__u32 *ptr = (__u32 *) regs;
- unsigned long flags;
+ unsigned int idx;
if (regs == NULL)
return 0;
- local_irq_save(flags);
- if (f->reg_idx >= sizeof(struct pt_regs) / sizeof(__u32))
- f->reg_idx = 0;
- ptr += f->reg_idx++;
- local_irq_restore(flags);
+ idx = READ_ONCE(f->reg_idx);
+ if (idx >= sizeof(struct pt_regs) / sizeof(__u32))
+ idx = 0;
+ ptr += idx++;
+ WRITE_ONCE(f->reg_idx, idx);
return *ptr;
}
Patches currently in stable-queue which might be from tytso@xxxxxxx are
queue-3.18/fix-race-in-drivers-char-random.c-get_reg.patch
queue-3.18/ext4-fix-off-by-one-on-max-nr_pages-in-ext4_find_unwritten_pgoff.patch
queue-3.18/random-use-lockless-method-of-accessing-and-updating-f-reg_idx.patch