From 031987b6beaa02f64aa4428329e34ee3c5b3c76f Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Wed, 7 Jun 2017 19:01:32 -0400 Subject: [PATCH] random: use lockless method of accessing and updating f->reg_idx 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 Cc: Michael Schmitz Signed-off-by: Greg Kroah-Hartman --- drivers/char/random.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 29b4218e9b63..bd9fc2baa6aa 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -886,15 +886,15 @@ static void add_interrupt_bench(cycles_t start) 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; } -- 2.11.0