Commit ce003d67 authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

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: b6cf8b3f ("printk: add lockless ringbuffer")
Signed-off-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200914094803.27365-1-john.ogness@linutronix.de
parent e6076831

kernel/printk/printk_ringbuffer.c

+19 −7
Original line number Diff line number Diff line
@@ -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;

}



/*

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