https://bugzilla.kernel.org/show_bug.cgi?id=215769 --- Comment #6 from brauner@xxxxxxxxxx --- On Sat, Apr 02, 2022 at 11:15:52PM +0200, Alejandro Colomar (man-pages) wrote: > [Added some kernel CCs that may know what's going on] > > Hi, > > On 3/31/22 09:53, bugzilla-daemon@xxxxxxxxxx wrote: > > https://bugzilla.kernel.org/show_bug.cgi?id=215769 > > > > --- Comment #3 from Коренберг Марк (socketpair@xxxxxxxxx) --- > > Hi, > > I appreciate depth of information validation. Actually, you are right. > vfork() > > DOES work with pid=1 processes. I figured out the cause in my case. In > order to > > reproduce -- add unshare(CLONE_NEWTIME) just before vfork(). Now, I don't > know > > if it's a bug in vfork() or in fork(). Yes, both are clone() actually. > > > > In any case, they should either both give EINVAL or both don't fail. But > it's > > definitely bug in the kernel around CLONE_NEWTIME. > > > > On 3/31/22 10:12, bugzilla-daemon@xxxxxxxxxx wrote: > > https://bugzilla.kernel.org/show_bug.cgi?id=215769 > > > > --- Comment #4 from Коренберг Марк (socketpair@xxxxxxxxx) --- > > #define _GNU_SOURCE 1 > > #include <stdio.h> > > #include <sched.h> > > #include <stdlib.h> > > #include <unistd.h> > > #include <sys/types.h> > > #include <sys/wait.h> > > #include <err.h> > > > > #ifndef CLONE_NEWTIME > > #define CLONE_NEWTIME 0x00000080 > > #endif > > > > int main (void) > > { > > if (unshare (CLONE_NEWTIME)) err (EXIT_FAILURE, "UNSHARE_NEWTIME"); > > > > pid_t pid; > > switch (pid=vfork ()) > > { > > case 0: > > _exit(0); > > case -1: > > err(EXIT_FAILURE, "vfork BUG"); > > default: > > waitpid(pid, NULL, 0); > > } > > return 0; > > } > > > > I could reproduce it with the following code. I tried > syscall(SYS_vfork) to make sure it's not a problem in the libc wrapper, > and to make sure I do call vfork(2). If I replace vfork(2) with > fork(2), I don't get the error. > > > $ cat vfork.c > #define _GNU_SOURCE > #include <err.h> > #include <linux/sched.h> > #include <sched.h> > #include <signal.h> > #include <stdlib.h> > #include <sys/syscall.h> > #include <unistd.h> > > int main(void) > { > pid_t pid; > > if (unshare(CLONE_NEWTIME) == -1) > err(EXIT_FAILURE, "unshare(2)"); > if (signal(SIGCHLD, SIG_IGN) == SIG_ERR) > err(EXIT_FAILURE, "sigaction(2)"); > pid = syscall(SYS_vfork); > switch (pid) { > case 0: > errx(EXIT_SUCCESS, "Grandchild exiting normally."); > case -1: > /* If we got here, the report is confirmed. */ > err(EXIT_FAILURE, "vfork(2)"); > default: > errx(EXIT_SUCCESS, "Child exiting normally."); > } > } > > $ cc -Wall -Wextra -Werror vfork.c > $ sudo ./a.out > a.out: vfork(2): Invalid argument > > > > $ grep_syscall_def vfork > kernel/fork.c:2711: > SYSCALL_DEFINE0(vfork) > { > struct kernel_clone_args args = { > .flags = CLONE_VFORK | CLONE_VM, > .exit_signal = SIGCHLD, > }; > > return kernel_clone(&args); > } > > > Maybe someone in the kernel can send some patch for the clone(2) and/or > vfork(2) manual pages that explains the reason (if it's intended). Hey Alejandro, I won't be able to send a patch very soon but I can at least explain why you see EINVAL. :) This is intended. vfork() suspends the parent process and the child process will share the same vm as the parent process. If the child process is in a new time namespace different from its parent process it is not allowed to be in the same threadgroup or share virtual memory with the parent process. That's why you see EINVAL. Note, the unshare(CLONE_NEWTIME) call will _not_ cause the calling process to be moved into a different time namespace. Only the newly created child process will be after a subsequent fork()/vfork()/clone()/clone3()... The semantics are equivalent to that of CLONE_NEWPID in this regard. You can see this via /proc/<pid>/ns/ where you see two entries for pid namespaces and also two entries for time namespaces: * CLONE_NEWTIME * /proc/<pid>/ns/time // current time namespace * /proc/<pid>/ns/time_for_children // time namespace for the new child process If during fork: parent_process->time != parent_process->time_for_children and either CLONE_VM or CLONE_THREAD is set you see EINVAL. You can thus replicate the same error via: unshare(CLONE_NEWTIME) and a clone() or clone3() call with CLONE_VM or CLONE_THREAD. Christian -- You may reply to this email to add a comment. You are receiving this mail because: You are watching the assignee of the bug.
