Serge E. Hallyn wrote: > Quoting Oren Laadan (orenl@xxxxxxxxxxxxxxx): >> >> Matt Helsley wrote: >>> Save and restore the [compat_]robust_list member of the task struct. >>> >>> These lists record which futexes the task holds. To keep the overhead of >>> robust futexes low the list is kept in userspace. When the task exits the >>> kernel carefully walks these lists to recover held futexes that >>> other tasks may be attempting to acquire with FUTEX_WAIT. >>> >>> Because they point to userspace memory that is saved/restored by >>> checkpoint/restart saving the list pointers works. >>> >>> While saving the pointers works during checkpoint, restart is tricky >>> because the robust futex ABI contains provisions for changes based on >>> checking the size of the list head. So we need to save the length of >>> the list head too in order to make sure that the kernel used during >>> restart is capable of handling that ABI. Since there is only one ABI >>> supported at the moment taking the list head's size is simple. Should >>> the ABI change we will need to use the same size as specified during >>> sys_set_robust_list() and hence some new means of determining the length >>> of this userspace structure in sys_checkpoint would be required. >>> >>> Rather than rewrite the logic that checks and handles the ABI we reuse >>> sys_set_robust_list() by factoring out the body of the function and >>> calling it during restart. >>> >>> Signed-off-by: Matt Helsley <matthltc@xxxxxxxxxx> >> Patch looks good. Too bad we don't support futex, yet... > > ? > > IIUC (from Matt and Dave), after this patch, you might need something > for PI futexes, but otherwise non-contended cases "just work" because > there is no kernel involvement. That's what I thought. But I also thought that a checkpoint would fail anyway as soon as it hits the futex-file-descriptor. Or am I missing something ? Oren. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
