From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Theodore Tso , Michael Schmitz Subject: [PATCH 4.9 274/310] random: use lockless method of accessing and updating f->reg_idx Date: Wed, 11 Apr 2018 20:36:53 +0200 Message-Id: <20180411183634.411401502@linuxfoundation.org> In-Reply-To: <20180411183622.305902791@linuxfoundation.org> References: <20180411183622.305902791@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Theodore Ts'o 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(-) --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1115,15 +1115,15 @@ 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; }