Messages in this thread | | | Date | Thu, 8 Sep 2022 10:54:42 -0400 | Subject | Re: [PATCH v7 4/5] sched: Handle set_cpus_allowed_ptr() & sched_setaffinity() race | From | Waiman Long <> |
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On 9/8/22 07:53, Peter Zijlstra wrote: > On Fri, Sep 02, 2022 at 11:25:55AM -0400, Waiman Long wrote: >> Racing is possible between set_cpus_allowed_ptr() and sched_setaffinity() >> or between multiple sched_setaffinity() calls from different >> CPUs. To resolve these race conditions, we need to update both >> user_cpus_ptr and cpus_mask in a single lock critical section instead >> of separated ones. This requires moving the user_cpus_ptr update to >> set_cpus_allowed_common(). >> >> The SCA_USER flag will be used to signify that a user_cpus_ptr update >> will have to be done. The new user_cpus_ptr will be put into the >> a percpu variable pending_user_mask at the beginning of the lock >> crtical section. The pending user mask will then be taken up in >> set_cpus_allowed_common(). >> >> Ideally, user_cpus_ptr should only be updated if the sched_setaffinity() >> is successful. However, this patch will update user_cpus_ptr when the >> first call to __set_cpus_allowed_ptr() is successful. However, if there >> is racing between sched_setaffinity() and cpuset update, the subsequent >> calls to __set_cpus_allowed_ptr() may fail but the user_cpus_ptr will >> still be updated in this corner case. A warning will be printed in this >> corner case. >> >> Signed-off-by: Waiman Long <longman@redhat.com> > OK, so obviously this is terrible :/ > > What's wrong with something like so ?
Thanks for the suggestion. I have no problem adding an affinity_context structure to pass around the functions. Will incorporate your suggestion in the next version of the patch.
Thanks, Longman
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