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printk: ringbuffer: fix setting state in desc_read()

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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: b6cf8b3f33 ("printk: add lockless ringbuffer")
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200914094803.27365-1-john.ogness@linutronix.de
This commit is contained in:
John Ogness 2020-09-14 11:54:02 +02:06 committed by Petr Mladek
parent e60768311a
commit ce003d67ad
1 changed files with 19 additions and 7 deletions
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26
kernel/printk/printk_ringbuffer.c
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@ -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;
}
/*