Previously, data blocks that perfectly fit the data ring buffer would
get wrapped around to the beginning for no reason since the calculated
offset of the next data block would belong to the next wrap. Since this
offset is not actually part of the data block, but rather the offset of
where the next data block is going to start, there is no reason to
include it when deciding whether the current block fits the buffer.
Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
---
kernel/printk/printk_ringbuffer.c | 27 +++++++++++++++++++--------
1 file changed, 19 insertions(+), 8 deletions(-)
diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
index d9fb053cff67..99989a9ce4b4 100644
--- a/kernel/printk/printk_ringbuffer.c
+++ b/kernel/printk/printk_ringbuffer.c
@@ -1002,6 +1002,17 @@ static bool desc_reserve(struct printk_ringbuffer *rb, unsigned long *id_out)
return true;
}
+static bool is_blk_wrapped(struct prb_data_ring *data_ring,
+ unsigned long begin_lpos, unsigned long next_lpos)
+{
+ /*
+ * Subtract one from next_lpos since it's not actually part of this data
+ * block. This allows perfectly fitting records to not wrap.
+ */
+ return DATA_WRAPS(data_ring, begin_lpos) !=
+ DATA_WRAPS(data_ring, next_lpos - 1);
+}
+
/* Determine the end of a data block. */
static unsigned long get_next_lpos(struct prb_data_ring *data_ring,
unsigned long lpos, unsigned int size)
@@ -1013,7 +1024,7 @@ static unsigned long get_next_lpos(struct prb_data_ring *data_ring,
next_lpos = lpos + size;
/* First check if the data block does not wrap. */
- if (DATA_WRAPS(data_ring, begin_lpos) == DATA_WRAPS(data_ring, next_lpos))
+ if (!is_blk_wrapped(data_ring, begin_lpos, next_lpos))
return next_lpos;
/* Wrapping data blocks store their data at the beginning. */
@@ -1081,7 +1092,7 @@ static char *data_alloc(struct printk_ringbuffer *rb, unsigned int size,
blk = to_block(data_ring, begin_lpos);
blk->id = id; /* LMM(data_alloc:B) */
- if (DATA_WRAPS(data_ring, begin_lpos) != DATA_WRAPS(data_ring, next_lpos)) {
+ if (is_blk_wrapped(data_ring, begin_lpos, next_lpos)) {
/* Wrapping data blocks store their data at the beginning. */
blk = to_block(data_ring, 0);
@@ -1125,7 +1136,7 @@ static char *data_realloc(struct printk_ringbuffer *rb, unsigned int size,
return NULL;
/* Keep track if @blk_lpos was a wrapping data block. */
- wrapped = (DATA_WRAPS(data_ring, blk_lpos->begin) != DATA_WRAPS(data_ring, blk_lpos->next));
+ wrapped = is_blk_wrapped(data_ring, blk_lpos->begin, blk_lpos->next);
size = to_blk_size(size);
@@ -1151,7 +1162,7 @@ static char *data_realloc(struct printk_ringbuffer *rb, unsigned int size,
blk = to_block(data_ring, blk_lpos->begin);
- if (DATA_WRAPS(data_ring, blk_lpos->begin) != DATA_WRAPS(data_ring, next_lpos)) {
+ if (is_blk_wrapped(data_ring, blk_lpos->begin, next_lpos)) {
struct prb_data_block *old_blk = blk;
/* Wrapping data blocks store their data at the beginning. */
@@ -1187,7 +1198,7 @@ static unsigned int space_used(struct prb_data_ring *data_ring,
if (BLK_DATALESS(blk_lpos))
return 0;
- if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next)) {
+ if (!is_blk_wrapped(data_ring, blk_lpos->begin, blk_lpos->next)) {
/* Data block does not wrap. */
return (DATA_INDEX(data_ring, blk_lpos->next) -
DATA_INDEX(data_ring, blk_lpos->begin));
@@ -1234,14 +1245,14 @@ static const char *get_data(struct prb_data_ring *data_ring,
}
/* Regular data block: @begin less than @next and in same wrap. */
- if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next) &&
+ if (!is_blk_wrapped(data_ring, blk_lpos->begin, blk_lpos->next) &&
blk_lpos->begin < blk_lpos->next) {
db = to_block(data_ring, blk_lpos->begin);
*data_size = blk_lpos->next - blk_lpos->begin;
/* Wrapping data block: @begin is one wrap behind @next. */
- } else if (DATA_WRAPS(data_ring, blk_lpos->begin + DATA_SIZE(data_ring)) ==
- DATA_WRAPS(data_ring, blk_lpos->next)) {
+ } else if (!is_blk_wrapped(data_ring,
+ blk_lpos->begin + DATA_SIZE(data_ring), blk_lpos->next)) {
db = to_block(data_ring, 0);
*data_size = DATA_INDEX(data_ring, blk_lpos->next);
--
2.43.0On 2025-09-05, Daniil Tatianin <d-tatianin@yandex-team.ru> wrote:
> diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
> index d9fb053cff67..99989a9ce4b4 100644
> --- a/kernel/printk/printk_ringbuffer.c
> +++ b/kernel/printk/printk_ringbuffer.c
> @@ -1234,14 +1245,14 @@ static const char *get_data(struct prb_data_ring *data_ring,
> }
>
> /* Regular data block: @begin less than @next and in same wrap. */
> - if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next) &&
> + if (!is_blk_wrapped(data_ring, blk_lpos->begin, blk_lpos->next) &&
> blk_lpos->begin < blk_lpos->next) {
> db = to_block(data_ring, blk_lpos->begin);
> *data_size = blk_lpos->next - blk_lpos->begin;
>
> /* Wrapping data block: @begin is one wrap behind @next. */
> - } else if (DATA_WRAPS(data_ring, blk_lpos->begin + DATA_SIZE(data_ring)) ==
> - DATA_WRAPS(data_ring, blk_lpos->next)) {
> + } else if (!is_blk_wrapped(data_ring,
> + blk_lpos->begin + DATA_SIZE(data_ring), blk_lpos->next)) {
It would look nicer if the arguments of the function were indented to
the function parenthesis:
} else if (!is_blk_wrapped(data_ring, blk_lpos->begin +
DATA_SIZE(data_ring), blk_lpos->next)) {
Otherwise, everything is OK for me.
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Tested-by: John Ogness <john.ogness@linutronix.de>
On 2025-09-05, John Ogness <john.ogness@linutronix.de> wrote:
>> diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
>> index d9fb053cff67..99989a9ce4b4 100644
>> --- a/kernel/printk/printk_ringbuffer.c
>> +++ b/kernel/printk/printk_ringbuffer.c
>> @@ -1234,14 +1245,14 @@ static const char *get_data(struct prb_data_ring *data_ring,
>> }
>>
>> /* Regular data block: @begin less than @next and in same wrap. */
>> - if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next) &&
>> + if (!is_blk_wrapped(data_ring, blk_lpos->begin, blk_lpos->next) &&
>> blk_lpos->begin < blk_lpos->next) {
>> db = to_block(data_ring, blk_lpos->begin);
>> *data_size = blk_lpos->next - blk_lpos->begin;
>>
>> /* Wrapping data block: @begin is one wrap behind @next. */
>> - } else if (DATA_WRAPS(data_ring, blk_lpos->begin + DATA_SIZE(data_ring)) ==
>> - DATA_WRAPS(data_ring, blk_lpos->next)) {
>> + } else if (!is_blk_wrapped(data_ring,
>> + blk_lpos->begin + DATA_SIZE(data_ring), blk_lpos->next)) {
>
> It would look nicer if the arguments of the function were indented to
> the function parenthesis:
>
> } else if (!is_blk_wrapped(data_ring, blk_lpos->begin +
> DATA_SIZE(data_ring), blk_lpos->next)) {
Ugh, my mail client messed that up. I meant to write:
} else if (!is_blk_wrapped(data_ring,
blk_lpos->begin + DATA_SIZE(data_ring),
blk_lpos->next)) {
> Reviewed-by: John Ogness <john.ogness@linutronix.de>
> Tested-by: John Ogness <john.ogness@linutronix.de>
On 9/5/25 6:27 PM, John Ogness wrote:
> On 2025-09-05, Daniil Tatianin <d-tatianin@yandex-team.ru> wrote:
>> diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
>> index d9fb053cff67..99989a9ce4b4 100644
>> --- a/kernel/printk/printk_ringbuffer.c
>> +++ b/kernel/printk/printk_ringbuffer.c
>> @@ -1234,14 +1245,14 @@ static const char *get_data(struct prb_data_ring *data_ring,
>> }
>>
>> /* Regular data block: @begin less than @next and in same wrap. */
>> - if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next) &&
>> + if (!is_blk_wrapped(data_ring, blk_lpos->begin, blk_lpos->next) &&
>> blk_lpos->begin < blk_lpos->next) {
>> db = to_block(data_ring, blk_lpos->begin);
>> *data_size = blk_lpos->next - blk_lpos->begin;
>>
>> /* Wrapping data block: @begin is one wrap behind @next. */
>> - } else if (DATA_WRAPS(data_ring, blk_lpos->begin + DATA_SIZE(data_ring)) ==
>> - DATA_WRAPS(data_ring, blk_lpos->next)) {
>> + } else if (!is_blk_wrapped(data_ring,
>> + blk_lpos->begin + DATA_SIZE(data_ring), blk_lpos->next)) {
> It would look nicer if the arguments of the function were indented to
> the function parenthesis:
>
> } else if (!is_blk_wrapped(data_ring, blk_lpos->begin +
> DATA_SIZE(data_ring), blk_lpos->next)) {
Would you like me to resend with this addressed?
Thanks!
> Otherwise, everything is OK for me.
>
> Reviewed-by: John Ogness <john.ogness@linutronix.de>
> Tested-by: John Ogness <john.ogness@linutronix.de>
On 2025-09-05, Daniil Tatianin <d-tatianin@yandex-team.ru> wrote:
> On 9/5/25 6:27 PM, John Ogness wrote:
>> On 2025-09-05, Daniil Tatianin <d-tatianin@yandex-team.ru> wrote:
>>> diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
>>> index d9fb053cff67..99989a9ce4b4 100644
>>> --- a/kernel/printk/printk_ringbuffer.c
>>> +++ b/kernel/printk/printk_ringbuffer.c
>>> @@ -1234,14 +1245,14 @@ static const char *get_data(struct prb_data_ring *data_ring,
>>> }
>>>
>>> /* Regular data block: @begin less than @next and in same wrap. */
>>> - if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next) &&
>>> + if (!is_blk_wrapped(data_ring, blk_lpos->begin, blk_lpos->next) &&
>>> blk_lpos->begin < blk_lpos->next) {
>>> db = to_block(data_ring, blk_lpos->begin);
>>> *data_size = blk_lpos->next - blk_lpos->begin;
>>>
>>> /* Wrapping data block: @begin is one wrap behind @next. */
>>> - } else if (DATA_WRAPS(data_ring, blk_lpos->begin + DATA_SIZE(data_ring)) ==
>>> - DATA_WRAPS(data_ring, blk_lpos->next)) {
>>> + } else if (!is_blk_wrapped(data_ring,
>>> + blk_lpos->begin + DATA_SIZE(data_ring), blk_lpos->next)) {
>> It would look nicer if the arguments of the function were indented to
>> the function parenthesis:
>>
>> } else if (!is_blk_wrapped(data_ring, blk_lpos->begin +
>> DATA_SIZE(data_ring), blk_lpos->next)) {
>
> Would you like me to resend with this addressed?
Knowing Petr, I would say "yes". :-)
But wait for Petr's response before sending anything.
John
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