From 67e1b0052f6bb82be84e30a5af7d27f29533a83b Mon Sep 17 00:00:00 2001 From: Daniil Tatianin Date: Fri, 5 Sep 2025 17:41:51 +0300 Subject: [PATCH] printk_ringbuffer: don't needlessly wrap data blocks around 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 Reviewed-by: Petr Mladek Tested-by: Petr Mladek Reviewed-by: John Ogness Tested-by: John Ogness Link: https://patch.msgid.link/20250905144152.9137-2-d-tatianin@yandex-team.ru [pmladek@suse.com: Updated indentation.] Signed-off-by: Petr Mladek --- kernel/printk/printk_ringbuffer.c | 28 ++++++++++++++++++++-------- 1 file changed, 20 insertions(+), 8 deletions(-) diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c index 40198bffb7d0d..839f504db6d30 100644 --- a/kernel/printk/printk_ringbuffer.c +++ b/kernel/printk/printk_ringbuffer.c @@ -999,6 +999,17 @@ 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) @@ -1010,7 +1021,7 @@ 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. */ @@ -1087,7 +1098,7 @@ 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); @@ -1131,7 +1142,7 @@ 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); @@ -1167,7 +1178,7 @@ 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. */ @@ -1203,7 +1214,7 @@ 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)); @@ -1250,14 +1261,15 @@ 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); -- 2.47.3