Re: [libvirt] [PATCH] virtlockd: acquire locks on re-exec

On Thu, Mar 01, 2018 at 04:42:36PM -0700, Jim Fehlig wrote: This is really strange and should *not* be happening. POSIX locks are supposed to be preserved across execve() if the FD has CLOEXEC unset, and you don't fork() before the exec. eg see this demo program: #include <stdio.h> #include <fcntl.h> #include <stdlib.h> #include <pthread.h> #include <unistd.h> int main(int argc, char **argv) { if (argc == 2) { int fd = atoi(argv[1]); struct flock fl = { .l_type = F_WRLCK, .l_whence = SEEK_SET, .l_start = 0, .l_len = 42, }; if (fcntl(fd, F_GETLK, &fl) < 0) abort(); int flags; if ((flags = fcntl(fd, F_GETFD)) < 0) abort(); flags |= FD_CLOEXEC; if (fcntl(fd, F_SETFD, flags) < 0) abort(); fprintf(stderr, "Owned %d\n", fl.l_pid); fprintf(stderr, "Execd\n"); sleep(50); } else { int fd = open("lock.txt", O_WRONLY|O_CREAT|O_TRUNC, 0755); if (fd < 0) abort(); struct flock fl = { .l_type = F_WRLCK, .l_whence = SEEK_SET, .l_start = 0, .l_len = 42, }; if (fcntl(fd, F_SETLK, &fl) < 0) abort(); int flags; if ((flags = fcntl(fd, F_GETFD)) < 0) abort(); flags &= ~FD_CLOEXEC; if (fcntl(fd, F_SETFD, flags) < 0) abort(); char fdstr[100]; snprintf(fdstr, sizeof(fdstr), "%d", fd); char *newargv[] = { argv[0], fdstr, NULL }; fprintf(stderr, "Waiting\n"); sleep(10); execve(argv[0], newargv, NULL); } } If you run this, you'll see the lock still exists after execveI(). So I wonder what we've screwed up to cause the locks to get released - reaquiring them definitely isn't desirable as we should not loose them in the first place ! Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|