From ce003d67ad521d950687bce7e42e5361022c7d3d Mon Sep 17 00:00:00 2001 From: John Ogness Date: Mon, 14 Sep 2020 11:54:02 +0206 Subject: [PATCH] printk: ringbuffer: fix setting state in desc_read() It is expected that desc_read() will always set at least the @state_var field. However, if the descriptor is in an inconsistent state, no fields are set. Also, the second load of @state_var is not stored in @desc_out and so might not match the state value that is returned. Always set the last loaded @state_var into @desc_out, regardless of the descriptor consistency. 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/20200914094803.27365-1-john.ogness@linutronix.de --- kernel/printk/printk_ringbuffer.c | 26 +++++++++++++++++++------- 1 file changed, 19 insertions(+), 7 deletions(-) diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c index 0659b50872b5..88f7dd4cb0c1 100644 --- a/kernel/printk/printk_ringbuffer.c +++ b/kernel/printk/printk_ringbuffer.c @@ -368,9 +368,9 @@ static enum desc_state get_desc_state(unsigned long id, } /* - * Get a copy of a specified descriptor and its queried state. A descriptor - * that is not in the committed or reusable state must be considered garbage - * by the reader. + * Get a copy of a specified descriptor and return its queried state. If the + * descriptor is in an inconsistent state (miss or reserved), the caller can + * only expect the descriptor's @state_var field to be valid. */ static enum desc_state desc_read(struct prb_desc_ring *desc_ring, unsigned long id, struct prb_desc *desc_out) @@ -383,8 +383,14 @@ static enum desc_state desc_read(struct prb_desc_ring *desc_ring, /* Check the descriptor state. */ state_val = atomic_long_read(state_var); /* LMM(desc_read:A) */ d_state = get_desc_state(id, state_val); - if (d_state != desc_committed && d_state != desc_reusable) - return d_state; + if (d_state == desc_miss || d_state == desc_reserved) { + /* + * The descriptor is in an inconsistent state. Set at least + * @state_var so that the caller can see the details of + * the inconsistent state. + */ + goto out; + } /* * Guarantee the state is loaded before copying the descriptor @@ -449,9 +455,15 @@ static enum desc_state desc_read(struct prb_desc_ring *desc_ring, */ smp_rmb(); /* LMM(desc_read:D) */ - /* Re-check the descriptor state. */ + /* + * The data has been copied. Return the current descriptor state, + * which may have changed since the load above. + */ state_val = atomic_long_read(state_var); /* LMM(desc_read:E) */ - return get_desc_state(id, state_val); + d_state = get_desc_state(id, state_val); +out: + atomic_long_set(&desc_out->state_var, state_val); + return d_state; } /*