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    SubjectRe: [PATCH] seqlock: serialize against writers

    On Fri, 29 Aug 2008, Gregory Haskins wrote:
    > Yeah, ideas crossed in the mail ;)
    > I could just force all of the seqbegins to hit the slowpath by hacking
    > the code and see what happens (aside from slowing down, of course ;)
    > Question: Which seqlock_t does userspace use? I assume it uses
    > seqlock_t and not raw_seqlock_t. But the only reason that I ask is that
    > I converted raw_seqlock_t to use the new style as well to be consistent,
    > even though it is not strictly necessary for the same reasons. So if
    > perchance userspace uses the raw variant, I could solve this issue by
    > only re-working the seqlock_t variant. Kind of a long shot, but figured
    > I would mention it :)

    I answered this on IRC, but this is for the rest of those reading this

    Userspace (vsyscalls) can only use raw_seqlock_t. And only the read
    version for that matter. Since the read of raw_seqlock_t is just that, a
    read, no writes, and no jumping to other functions on contention.

    The vsyscalls should never use the -rt seqlock_t. Not modifying the raws
    here should make us golden.

    -- Steve

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      Last update: 2008-08-29 19:01    [W:0.031 / U:100.384 seconds]
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