[lkml]   [2008]   [Nov]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [PATH -mm -v2] Fix a race condtion of oops_in_progress
    On Sat, 2008-11-01 at 00:42 +0800, Chris Snook wrote:
    > Huang Ying wrote:
    > > Hi, Chris,
    > >
    > > On Wed, 2008-10-29 at 08:51 -0600, Chris Snook wrote:
    > >> Huang Ying wrote:
    > >>> Fix a race condition accessing oops_in_progress. Which may be changed on
    > >>> multiple CPU simultaneously, but it is changed via non-atomic operation
    > >>> ++/--. This patch changes the definition of oops_in_process from int to
    > >>> atomic_t, and accessing method to atomic operations.
    > >> You also need barriers. I believe rmb() before atomic_read() and wmb() after
    > >> atomic_set() should suffice.
    > >
    > > I don't think that is necessary. I haven't found there is particular
    > > consistent requirement about oops_in_progress.
    > atomic_read() and atomic_set() don't inherently cause changes to be visible on
    > other CPUs any faster than ++ and -- operators. Sometimes it happens to work
    > out that way as a result of how the compiler and the CPU order operations, but
    > there's no semantic guarantee, and it could even take arbitrarily long under
    > some circumstances. If you want to use atomic ops to close the race, you need
    > to use barriers.

    As far as I know, barriers don't cause changes to be visible on other
    CPUs faster too. It just guarantees corresponding operations after will
    not get executed until that before have finished. And, I don't think we
    need make changes to be visible on other CPUs faster.

    Best Regards,
    Huang Ying

    [unhandled content-type:application/pgp-signature]
     \ /
      Last update: 2008-11-03 02:55    [W:0.023 / U:9.336 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site