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 <tytso@mit.edu>
Cc: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 23f3fb4..0c23ced 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1115,15 +1115,15 @@
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;
}