On Thu, Mar 01, 2018 at 04:42:36PM -0700, Jim Fehlig wrote:
> Locks held by virtlockd are dropped on re-exec.
>
> virtlockd 94306 POSIX 5.4G WRITE 0 0 0 /tmp/test.qcow2
> virtlockd 94306 POSIX 5B WRITE 0 0 0 /run/virtlockd.pid
> virtlockd 94306 POSIX 5B WRITE 0 0 0 /run/virtlockd.pid
>
> Acquire locks in PostExecRestart code path.
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 !
>
> Signed-off-by: Jim Fehlig <jfehlig@xxxxxxxx>
> ---
>
> The CLOEXEC flag is set in virLockSpaceNewPostExecRestart(), so I assume
> it is fine to call virFileLock() here as well.
>
> src/util/virlockspace.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/src/util/virlockspace.c b/src/util/virlockspace.c
> index 41af0cdb6..420878b0a 100644
> --- a/src/util/virlockspace.c
> +++ b/src/util/virlockspace.c
> @@ -337,6 +337,7 @@ virLockSpacePtr virLockSpaceNewPostExecRestart(virJSONValuePtr object)
> virJSONValuePtr owners;
> size_t j;
> ssize_t m;
> + bool shared = false;
>
> if (VIR_ALLOC(res) < 0)
> goto error;
> @@ -389,6 +390,21 @@ virLockSpacePtr virLockSpaceNewPostExecRestart(virJSONValuePtr object)
> goto error;
> }
>
> + shared = !!(res->flags & VIR_LOCK_SPACE_ACQUIRE_SHARED);
> + if (virFileLock(res->fd, shared, 0, 1, false) < 0) {
> + if (errno == EACCES || errno == EAGAIN) {
> + virReportError(VIR_ERR_RESOURCE_BUSY,
> + _("Lockspace resource '%s' is locked"),
> + res->name);
> + } else {
> + virReportSystemError(errno,
> + _("Unable to acquire lock on '%s'"),
> + res->path);
> + }
> + virLockSpaceResourceFree(res);
> + goto error;
> + }
> +
> if (!(owners = virJSONValueObjectGet(child, "owners"))) {
> virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> _("Missing resource owners in JSON document"));
> --
> 2.16.2
>
> --
> libvir-list mailing list
> libvir-list@xxxxxxxxxx
> https://www.redhat.com/mailman/listinfo/libvir-list
Regards,
Daniel
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