Re: [PATCH] Describe race of direct read and fork for unaligned buffers

From: Nick Piggin
Date: Tue May 08 2012 - 19:10:53 EST

On 6 May 2012 01:29, KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx> wrote:
>> So, am I correct to assume that right text to add to the page is as below?
>> Nick, can you clarify what you mean by "quiesced"?
> finished?

Yes exactly. That might be a simpler word. Thanks!

>> [[
>> O_DIRECT IOs should never be run concurrently with fork(2) system call,
>> when the memory buffer is anonymous memory, or comes from mmap(2)
>> with MAP_PRIVATE.
>> Any such IOs, whether submitted with asynchronous IO interface or from
>> another thread in the process, should be quiesced before fork(2) is called.
>> Failure to do so can result in data corruption and undefined behavior in
>> parent and child processes.
>> This restriction does not apply when the memory buffer for the O_DIRECT
>> IOs comes from mmap(2) with MAP_SHARED or from shmat(2).
>> Nor does this restriction apply when the memory buffer has been advised
>> as MADV_DONTFORK with madvise(2), ensuring that it will not be available
>> to the child after fork(2).
>> ]]
> I don't have good English and I can't make editorial check. But at least,
> I don't find any technical incorrect explanation here.
> ÂAcked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at