Re: [PATCH 1/2] cryo: re-enable checkpointing of thread area

["Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Quoting Benjamin Thery (benjamin.thery-6ktuUTfB/bM@public.gmane.org):
> This patch re-enable the code that checkpoints (and restore) and thread
> area (ldt) using ptrace_get_thread_area(). This is seem to improve the 
> situation a lot on systems with NPTL: it solved one of the general 
> protection fault I had when restarting a program.
> 
> Signed-off-by: Benjamin Thery <benjamin.thery-6ktuUTfB/bM@public.gmane.org>

Benjamin, you rock.  This fixes my kvm image as well.

Nadia, Suka, could you confirm that this does *not* break cryo on your
systems?

Patched added to git tree.

thanks,
-serge

> ---
>  cr.c |   17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
> 
> Index: cryodev/cr.c
> ===================================================================
> --- cryodev.orig/cr.c
> +++ cryodev/cr.c
> @@ -24,7 +24,7 @@
>  #include <signal.h>
>  #include <errno.h>
> 
> -#include <asm/ldt.h>	/* for redhat 9.0, NPTL */
> +#include <asm/ldt.h>	/* for NPTL */
> 
>  #include "utils.h"
>  #include "sci.h"
> @@ -513,14 +513,12 @@ static int save_process_data(pid_t pid, 
>  		return 0;
>  	}
> 
> -	/* This is required in redhat9 */
> -#if 0
> +	/* This is required for NPTL */
>  	{
> -		modify_ldt_t ldt;
> +		struct user_desc ldt;
>  		if (ptrace_get_thread_area(pid, &ldt) == 0)
>  			write_item(fd, "ldt", (void *)&ldt, sizeof(ldt));
>  	}
> -#endif
> 
>  	snprintf(fname, sizeof(fname), "/proc/%u/exe", pid);
>  	memset(exe, 0, sizeof(exe));
> @@ -1237,7 +1235,7 @@ static int process_restart(int fd, int m
>  	char *exe = NULL, *cwd = NULL, *sargv = NULL, *senv = NULL;
>  	struct user_regs_struct *regs = NULL;
>  	struct user_fpregs_struct *fpregs = NULL;
> -	//modify_ldt_t *ldt = NULL;
> +	struct user_desc *ldt = NULL;
>  	int *exitsig = NULL;
>  	sigset_t *sigmask = NULL, *sigpend = NULL;
>  	struct sigaction *sigact = NULL;
> @@ -1262,7 +1260,7 @@ static int process_restart(int fd, int m
>  			Free(senv);
>  			Free(regs);
>  			Free(fpregs);
> -			//Free(ldt);
> +			Free(ldt);
>  			Free(sigact);
>  			Free(sigmask);
>  			Free(sigpend);
> @@ -1276,7 +1274,7 @@ static int process_restart(int fd, int m
>  		else ITEM_SET(cwd, char);
>  		else ITEM_SET(regs, struct user_regs_struct);
>  		else ITEM_SET(fpregs, struct user_fpregs_struct);
> -		//else ITEM_SET(ldt, modify_ldt_t);
> +		else ITEM_SET(ldt, struct user_desc);
>  		else ITEM_SET(sigact, struct sigaction);
>  		else ITEM_SET(sigmask, sigset_t);
>  		else ITEM_SET(sigpend, sigset_t);
> @@ -1304,7 +1302,8 @@ static int process_restart(int fd, int m
>  				ERROR("lh_hash_add(%p, %u, %p)\n", &hpid, (unsigned)*pid, (void *)npid);
>  				return -1;
>  			}
> -			//if (ldt) ptrace_set_thread_area(npid, ldt);
> +			if (ldt)
> +				ptrace_set_thread_area(npid, ldt);
>  			if (cwd) PT_CHDIR(npid, cwd);
>  			restore_fd(fd, npid);
>  		} else if (ITEM_IS("SOCK")) {
> 
> --