| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.4 163/190] random: use lockless method of accessing and updating f->reg_idx | Date | Wed, 11 Apr 2018 20:36:49 +0200 |
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4.4-stable review patch. If anyone has any objections, please let me know.
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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 @@ -886,15 +886,15 @@ 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; }
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