On 03/08/2021 22:52, Paolo Bonzini wrote:
On Tue, Aug 3, 2021 at 1:16 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
On Fri, Jul 30, 2021 at 02:32:17PM +1000, Alexey Kardashevskiy wrote:
snprintf(dir_name, sizeof(dir_name), "%d-%d", task_pid_nr(current), fd);
kvm->debugfs_dentry = debugfs_create_dir(dir_name, kvm_debugfs_dir);
+ if (IS_ERR_OR_NULL(kvm->debugfs_dentry)) {
+ pr_err("Failed to create %s\n", dir_name);
+ return 0;
+ }
It should not matter if you fail a debugfs call at all.
If there is a larger race at work here, please fix that root cause, do
not paper over it by attempting to have debugfs catch the issue for you.
I don't think it's a race, it's really just a bug that is intrinsic in how
the debugfs files are named. You can just do something like this:
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <sys/ioctl.h>
#include <linux/kvm.h>
#include <stdlib.h>
int main() {
int kvmfd = open("/dev/kvm", O_RDONLY);
int fd = ioctl(kvmfd, KVM_CREATE_VM, 0);
if (fork() == 0) {
printf("before: %d\n", fd);
sleep(2);
} else {
close(fd);
sleep(1);
int fd = ioctl(kvmfd, KVM_CREATE_VM, 0);
printf("after: %d\n", fd);
wait(NULL);
}
}
oh nice demo :)
although I still think there was a race when I saw it as there was no
fork() in the picture but continuous create/destroy VM in 16 threads on
16 VCPUs with no KVM_RUN in between.
So Alexey's patch is okay and I've queued it, though with pr_warn_ratelimited
instead of pr_err.
Makes sense with your reproducer. Thanks,
--
Alexey
