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. -serge _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
