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SubjectRe: [PATCH 1/4] input: Introduce buflock, a one-to-many circular buffer mechanism
>> +#define buflock_write(bw, buf, size, item)				\
>> + do { \
>> + bw.next_head = (bw.head + 1) & ((size) - 1); \
>> + smp_wmb(); \
>
> Why do we need the write barrier here?

I believe my first answer to this question was foggy indeed, so allow me to go
again, with a time line:

Scenario 1, correct write order:

writer store_next_head store_buf store_head
reader load_head load_buf load_next_head

Result: head != next_head, incoherent read detected

Scenario 2, incorrect write order:

writer store_buf store_next_head store_head
reader load_head load_buf load_next_head

Result: head == next_head, incoherent read not detected

Based on the assumption that scenario 2 could happen if the smp_wmb() is not
present, the barrier is needed.

Henrik


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