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 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
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-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From 92e75428ffc90e2a0321062379f883f3671cfebe Mon Sep 17 00:00:00 2001
From: Theodore Ts'o tytso@mit.edu 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@mit.edu
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
--- 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; }
Patches currently in stable-queue which might be from tytso@mit.edu are
queue-4.9/fix-race-in-drivers-char-random.c-get_reg.patch queue-4.9/ext4-handle-the-rest-of-ext4_mb_load_buddy-enomem-errors.patch queue-4.9/ext4-fix-off-by-one-on-max-nr_pages-in-ext4_find_unwritten_pgoff.patch queue-4.9/random-use-lockless-method-of-accessing-and-updating-f-reg_idx.patch