Re: [PATCH] Describe race of direct read and fork for unaligned buffers
From: Jan Kara <hidden>
Date: 2012-05-02 09:20:35
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linux-mm, lkml
On Tue 01-05-12 20:04:15, Hugh Dickins wrote:
On Wed, 2 May 2012, Nick Piggin wrote:quoted
On 2 May 2012 03:56, Michael Kerrisk (man-pages) [off-list ref] wrote:quoted
In the light of all of the comments, can someone revise the man-pages patch that Jan sent?This does not quite describe the entire situation, but something understandable to developers: 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).
Yes, I think with this addition the text is fine. Honza -- Jan Kara [off-list ref] SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html