random: use lockless method of accessing and updating f->reg_idx (92e75428) · Commits · 戴 / test

Linus pointed out that there is a much more efficient way of avoiding the problem that we were trying to address in commit : "fix race in drivers/char/random.c:get_reg()". Signed-off-by:

Theodore Ts'o <tytso@mit.edu>

drivers/char/random.c

+6 −6

Original line number	Diff line number	Diff line
		@@ -1097,15 +1097,15 @@ 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;
		}

Admin message