From: John Ogness Date: Mon, 14 Sep 2020 09:48:03 +0000 (+0206) Subject: printk: ringbuffer: avoid memcpy() on state_var X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=e7c1fe21046a024a5a9ef46e3752521afc1ada7b;p=linux.git printk: ringbuffer: avoid memcpy() on state_var @state_var is copied as part of the descriptor copying via memcpy(). This is not allowed because @state_var is an atomic type, which in some implementations may contain a spinlock. Avoid using memcpy() with @state_var by explicitly copying the other fields of the descriptor. @state_var is set using atomic set operator before returning. Fixes: b6cf8b3f3312 ("printk: add lockless ringbuffer") Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20200914094803.27365-2-john.ogness@linutronix.de --- diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c index 88f7dd4cb0c1e..11b860ad52643 100644 --- a/kernel/printk/printk_ringbuffer.c +++ b/kernel/printk/printk_ringbuffer.c @@ -412,9 +412,14 @@ static enum desc_state desc_read(struct prb_desc_ring *desc_ring, /* * Copy the descriptor data. The data is not valid until the - * state has been re-checked. + * state has been re-checked. A memcpy() for all of @desc + * cannot be used because of the atomic_t @state_var field. */ - memcpy(desc_out, desc, sizeof(*desc_out)); /* LMM(desc_read:C) */ + memcpy(&desc_out->info, &desc->info, sizeof(desc_out->info)); /* LMM(desc_read:C) */ + memcpy(&desc_out->text_blk_lpos, &desc->text_blk_lpos, + sizeof(desc_out->text_blk_lpos)); /* also part of desc_read:C */ + memcpy(&desc_out->dict_blk_lpos, &desc->dict_blk_lpos, + sizeof(desc_out->dict_blk_lpos)); /* also part of desc_read:C */ /* * 1. Guarantee the descriptor content is loaded before re-checking