On Tue 2020-07-21 15:31:28, John Ogness wrote:
> With commit ("printk: use the lockless ringbuffer"), printk()
> started silently dropping messages without text because such
> records are not supported by the new printk ringbuffer.
>
> Add support for such records.
>
> Currently dataless records are denoted by INVALID_LPOS in order
> to recognize failed prb_reserve() calls. Change the ringbuffer
> to instead use two different identifiers (FAILED_LPOS and
> NO_LPOS) to distinguish between failed prb_reserve() records and
> successful dataless records, respectively.
>
> diff --git a/kernel/printk/printk_ringbuffer.c
> b/kernel/printk/printk_ringbuffer.c
> index 7355ca99e852..0659b50872b5 100644
> --- a/kernel/printk/printk_ringbuffer.c
> +++ b/kernel/printk/printk_ringbuffer.c
> static bool data_check_size(struct prb_data_ring *data_ring, unsigned int
> size)
> {
> struct prb_data_block *db = NULL;
>
> - /*
> - * Writers are not allowed to write data-less records. Such records
> - * are used only internally by the ringbuffer to denote records where
> - * their data failed to allocate or have been lost.
> - */
> if (size == 0)
> - return false;
> + return true;
Nit: This might deserve a comment why size == 0 is handled
a special way.specially. I think about something like:
/*
* Empty data blocks are handled by special lpos values in
* the record descriptor. No space is needed in the data ring.
*/
or simply
/* Data-less records take no space in the data ring. */
> /*
> * Ensure the alignment padded size could possibly fit in the data
> @@ -1025,6 +1020,10 @@ static char *data_alloc(struct printk_ringbuffer *rb,
> static unsigned int space_used(struct prb_data_ring *data_ring,
> struct prb_data_blk_lpos *blk_lpos)
> {
> + /* Data-less blocks take no space. */
> + if (LPOS_DATALESS(blk_lpos->begin))
> + return 0;
Nit: It seems that all the other locations check also blk_lpos->next,
for example, get_data() does:
if (LPOS_DATALESS(blk_lpos->begin) && LPOS_DATALESS(blk_lpos->next)) {
Both approaches are error prone. I would either simplify the
other locations and check only lpos->begin. But better might
be to be on the safe side do a paranoid check, like:
bool is_dataless(struct prb_data_blk_lpos *blk_lpos)
{
if (LPOS_DATALESS(blk_lpos->begin) || LPOS_DATALESS(blk_lpos->next)) {
WARN_ON_ONCE(blk_lpos->begin != blk_lpos->next);
return true;
}
return false;
}
> +
> if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring,
> blk_lpos->next)) {
> /* Data block does not wrap. */
> return (DATA_INDEX(data_ring, blk_lpos->next) -
Anyway, the patch looks fine. It is already pushed in
printk/linux.git. So, if you agree with my nits, we should
solve them with separate patches on top of the existing ones.
Best Regards,
Petr
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