diff options
| author | John Ogness <john.ogness@linutronix.de> | 2020-09-14 11:54:02 +0206 |
|---|---|---|
| committer | Petr Mladek <pmladek@suse.com> | 2020-09-15 14:23:37 +0200 |
| commit | ce003d67ad521d950687bce7e42e5361022c7d3d (patch) | |
| tree | 0b131518cfd2868d2780a1ddb70f16c30c51d1ef | |
| parent | e60768311af854734ce2bbfc50f24cff67b54a91 (diff) | |
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 <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
| -rw-r--r-- | kernel/printk/printk_ringbuffer.c | 26 |
1 files 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; } /* |