Nathan Lynch wrote: > On Thu, 2009-11-26 at 10:10 -0500, Oren Laadan wrote: >> Nathan Lynch wrote: >>> The feeder thread can cause the restart process to fail by indirectly >>> calling exit_group, which sends SIGKILL to all other threads in the >>> process. If the feeder thread "wins" the race, the restart is >>> disrupted. A common symptom of this race is the coordinator task >>> returning from the wait_for_completion_interruptible in >>> wait_all_tasks_finish with a signal (the SIGKILL) pending. >> So the clone mage page says: >> ... >> The main use of clone() is to implement threads: multiple threads >> of control in a program that run concurrently in a shared memory >> space. >> ... >> When the fn(arg) function application returns, the child process >> terminates. The integer returned by fn is the exit code for the >> child process. The child process may also terminate explicitly by >> calling exit(2) or after receiving a fatal signal. >> ... >> (http://www.kernel.org/doc/man-pages/online/pages/man2/__clone2.2.html) >> >> I expected "terminates" here to mean invoke the syscall _exit(). >> Clearly this is desirable with CLONE_THREAD, > > Calling _exit (as glibc's clone support code does) is clearly > undesirable for CLONE_THREAD users such as restart.c because _exit calls > exit_group, terminating the whole thread group. That's kind of the > whole point of the patch :) I did say "syscall _exit()" to distinguish from libc's _exit()... Anyway, we agree on the necessity of the patch. > > >> but not for regular >> processes that will want to proceed to the usual glibc exit path >> (e.g. process at_exit() and what-not). Then again, the last thread >> to exit should also call glibc's exit for the same reason. So >> that's probably why it's handled this way. >> >> This matters for us because our user-space wrapper to eclone() >> should eventually do what the glibc's clone() wrapper does, instead >> of calling _exit() directly as it is today... > > For compatibility's sake, the user-space eclone wrapper should > eventually do what glibc's clone support code does, yes -- branch to > _exit. But I think you've stated the case backwards? Currently the > eclone wrappers call sys_exit directly (e.g. "li r0,__NR_exit; sc" on > powerpc). Exactly: currently our wrapper calls the syscall _exit() directly, while the correct behavior which is expected by the user is the one provided by libc, that is - call libc's _exit() instead. So we should fix our wrappers... Oren. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
