Quoting Oren Laadan (orenl@xxxxxxxxxxxxxxx): > > > Serge E. Hallyn wrote: > > (This is a patch against the checkpoint/restart kernel tree at > > http://git.ncl.cs.columbia.edu/?p=linux-cr.git;a=shortlog;h=refs/heads/ckpt-v19-rc2.9) > > > > On x86, do_signal() leaves -516 in eax while it freezes, which > > sys_restart() can use to detect that it should restart the > > syscall which was interrupted by a signal (or the freezer). > > > > On s390, gprs[2] gets tweaked to -EINTR (-4) instead, leaving > > us no reliable way to tell whether should be restarted. If the > > task is checkpointed here and then restarted, then the last part > > of do_signal() won't be done, and the interrupted syscall won't > > be restarted. > > > > This patch defines TIF_RESTARTBLOCK as a thread flag showing that > > the thread expects to be frozen while kicked out of a restartable > > syscall by a signal. > > > > The TIF_RESTARTBLOCK flag is only set for the duration of the > > get get_signal_to_deliver() which is where the task may get > > frozen. We also set it in sys_restart() if the checkpointed task > > had had TIF_RESTARTBLOCK set. It will get cleared if upon exiting > > sys_restart() we jump to sysc_sigpending. If instead we jump back > > to do_signal(), then TIF_RESTARTBLOCK will stay set again until > > after get_signal_to_deliver() so that if it immediately freezes and > > is re-checkpointed, the resulting second checkpoint image again > > will have TIF_RESTARTBLOCK set. > > Two comments: > > 1) This note will be lost once we fold this patch into a clean > patchset. Can you please make it part of the code ? Sure, good idea. > 2) Maybe I'm missing something, but I'm not convinced. Can you > elaborate on why this is correct in different cases ? Also, in > particular with respect to the post-signal-sent snippet in the > signal handling code: > > if (retval == -ERESTART_RESTARTBLOCK > && regs->psw.addr == continue_addr) { > > regs->gprs[2] = __NR_restart_syscall; > > set_thread_flag(TIF_RESTART_SVC); > > } > > > Would it do what you expect after a restart ? (restart modifies > the psw.addr) I don't understand the question. After sys_restart(), we won't be returning to this kernel code. We'll either immediately call restart_syscall(), or, if a signal was delivered before sys_restart(), completed, then do_signal() will start again from the top. In the first case we're doing exactly what we wanted to. In that second case, we enter do_signal with very different initial conditions than the checkpointed case: regs->svcnr is 0, so none of the gprs[2] or svcnr or psw-addr tweaking that would have happened the first time will happen. We'll just handle the signal (if any), then, upon exit of do_signal, proceed again with regs->gprs[2] == __NR_restart_syscall. But, since thread_info_flags->TIF_RESTARTBLOCK is set, if we get frozen and checkpointed again during the get_signal_to_deliver(), a restart of that image should be exactly the same as a restart of the current image. (That, at least, is my intent and understanding :) -serge _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
