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SubjectRe: [PATCH 14/25] aio: Make aio_read_evt() more efficient
> We can't use cmpxchg() on the ring buffer's head pointer directly, since
> it's modded to nr_events and would be susceptible to ABA. So instead we
> maintain a shadow head that uses the full 32 bits, and cmpxchg() that
> and then updated the real head pointer.

Time to update this comment to reflect the mutex instead of the shadow
head? :)

> + ev = kmap(page);
> + copy_ret = copy_to_user(event + ret, ev + pos, sizeof(*ev) * i);
> + kunmap(page);

For lack of a better time: do we want to bring up the missing
flush_dcache_page() calls around the kernel mappings of ring pages that
are also mapped to user addresses?

> prepare_to_wait_exclusive(&ctx->wait, &wait,
> TASK_INTERRUPTIBLE);
>
> + ret = aio_read_events(ctx, event + i, nr - i);
> + if (ret < 0)
> break;

As mentioned offlist: we don't want to be blocking under
TASK_INTERRUPTIBLE. Is the plan to do a non-blocking check and pop
outside the wait loop to do a blocking copy?

- z


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