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Date: Wed, 18 Feb 2015 14:10:07 +0100
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Subject: Re: [Qemu-devel] [RFC PATCH v9 15/23] aio: replace stack of bottom
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To: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>, qemu-devel@nongnu.org
Cc: peter.maydell@linaro.org, peter.crosthwaite@xilinx.com, alex.bennee@linaro.org, mark.burton@greensocs.com, real@ispras.ru, batuzovk@ispras.ru, maria.klimushenkova@ispras.ru, afaerber@suse.de, fred.konrad@greensocs.com



On 18/02/2015 12:57, Pavel Dovgalyuk wrote:
> +#define QSIMPLEQ_INSERT_TAIL_RCU(head, elm, field) do {                 \
> +    (elm)->field.sqe_next = NULL;                                       \

Also, smp_wmb() goes here.

My fault: in the previous review I wrote "smp_wmb() must be after the
(elm) assignment". I meant after the assignment of elm's fields (i.e.
write elm's fields before publishing it) but it wasn't clear at all.

Even better, you can replace the following two lines with:

    atomic_rcu_set((head)->sqh_last, (elm));

Paolo

> +    *(head)->sqh_last = (elm);                                          \
> +    smp_wmb();                                                          \

> +    (head)->sqh_last = &(elm)->field.sqe_next;                          \
> +} while (/*CONSTCOND*/0)
> +