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printk_ringbuffer: Avoid needless read of prb_desc

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Since commit f244b4dc53 ("printk: ringbuffer: Improve prb_next_seq()
performance"), desc_read() allows @desc_out to be NULL. We can drop the
local `desc` variable in desc_reopen_last() and prb_first_seq(). Also
update the comment for desc_read().

v1->v2:
Update the comment suggested by John.

Signed-off-by: Wang Wensheng <wsw9603@163.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20260926094502.251204-1-wsw9603@163.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
This commit is contained in:
Wang Wensheng 2026-09-26 17:45:02 +08:00 committed by Petr Mladek
parent 731383dcf5
commit 267f1127c0
1 changed files with 7 additions and 10 deletions
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17
kernel/printk/printk_ringbuffer.c
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@ -439,13 +439,12 @@ static enum desc_state get_desc_state(unsigned long id,
}
/*
* 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.
* Get the state of a specified descriptor.
*
* The sequence number and caller_id can be optionally retrieved. Like all
* non-state_var data, they are only valid if the descriptor is in a
* consistent state.
* Optionally, a copy of the descriptor, sequence number and/or caller ID can
* be retrieved. However, (with the exception of @desc_out->state_var) all
* retrieved values are invalid if the descriptor is in an inconsistent state
* (miss or reserved).
*/
static enum desc_state desc_read(struct prb_desc_ring *desc_ring,
unsigned long id, struct prb_desc *desc_out,
@ -1335,7 +1334,6 @@ static struct prb_desc *desc_reopen_last(struct prb_desc_ring *desc_ring,
{
unsigned long prev_state_val;
enum desc_state d_state;
struct prb_desc desc;
struct prb_desc *d;
unsigned long id;
u32 cid;
@ -1346,7 +1344,7 @@ static struct prb_desc *desc_reopen_last(struct prb_desc_ring *desc_ring,
* To reduce unnecessarily reopening, first check if the descriptor
* state and caller ID are correct.
*/
d_state = desc_read(desc_ring, id, &desc, NULL, &cid);
d_state = desc_read(desc_ring, id, NULL, NULL, &cid);
if (d_state != desc_committed || cid != caller_id)
return NULL;
@ -2007,14 +2005,13 @@ u64 prb_first_seq(struct printk_ringbuffer *rb)
{
struct prb_desc_ring *desc_ring = &rb->desc_ring;
enum desc_state d_state;
struct prb_desc desc;
unsigned long id;
u64 seq;
for (;;) {
id = atomic_long_read(&rb->desc_ring.tail_id); /* LMM(prb_first_seq:A) */
d_state = desc_read(desc_ring, id, &desc, &seq, NULL); /* LMM(prb_first_seq:B) */
d_state = desc_read(desc_ring, id, NULL, &seq, NULL); /* LMM(prb_first_seq:B) */
/*
* This loop will not be infinite because the tail is