I can't recall a convincing reason why restore_{thread,cpu}() should
run so late, or in particular after restore_task_objs().
I think the original motivation was to avoid the point-of-no-return
at a very early stage. However this is only useful for self-restart.
If we ever want self-restart to fail gracefully should something go
wrong, we should be prepared to undo any changes to the process -
on the error path. While not beyond reach, it isn't a top priority.
Does calling restore_{thread,cpu}() earlier solve the problem ?
BTW, this is also relevant for x86-64...
Oren.
Serge E. Hallyn wrote:
> The arch-specific restore_thread() and restore_cpu() are called after
> restore_task_obj()s. This means that when a 32-bit task calls
> sys_restart() with a 64-bit image, we'll be reloading memory mappings
> before those are called, and get a 'mysterious' -EINVAL for trying to
> map libc into an area > TASK_SIZE.
>
> This patch just adds a set of arch-specific flags to the cpu_hdr_task
> struct. s390 can use this to note TIF_31BIT, and powerpc uses it to
> mark TIF_32BIT.
>
> With this patch, a 32-bit task restarting a 64-bit image at least gets
> a meaningful message in the user logfile and syslog:
> 32-bit task trying to restart a 64-bit one
>
> If we keep this patch, then we'll want to drop bitness_test from
> restore_cpu() in powerpc, and maybe use that code instead of the code
> I used. We also may eventually want to actually switch the task
> personality.
>
> Signed-off-by: Serge Hallyn <serue@xxxxxxxxxx>
> ---
> arch/powerpc/mm/checkpoint.c | 30 ++++++++++++++++++++++++++++++
> arch/s390/mm/checkpoint.c | 10 ++++++++++
> arch/x86/mm/checkpoint.c | 10 ++++++++++
> checkpoint/process.c | 6 ++++++
> include/linux/checkpoint.h | 6 ++++++
> include/linux/checkpoint_hdr.h | 1 +
> 6 files changed, 63 insertions(+), 0 deletions(-)
>
> diff --git a/arch/powerpc/mm/checkpoint.c b/arch/powerpc/mm/checkpoint.c
> index de18467..ec758d9 100644
> --- a/arch/powerpc/mm/checkpoint.c
> +++ b/arch/powerpc/mm/checkpoint.c
> @@ -207,6 +207,13 @@ static void checkpoint_dabr(struct ckpt_hdr_cpu *cpu_hdr,
> ckpt_cpu_feature_set(cpu_hdr, CKPT_USED_DEBUG);
> }
>
> +/* called early to set TIF_32BIT etc */
> +void checkpoint_arch_thread(struct ckpt_hdr_task *h, struct task_struct *t)
> +{
> + if (test_tsk_thread_flag(t, TIF_32BIT))
> + h->arch_flags |= CKPT_ARCH_32BIT;
> +}
> +
> /* dump the thread_struct of a given task */
> int checkpoint_thread(struct ckpt_ctx *ctx, struct task_struct *t)
> {
> @@ -264,6 +271,29 @@ int checkpoint_mm_context(struct ckpt_ctx *ctx, struct mm_struct *mm)
> * Restart
> */
>
> +/*
> + * Called early to check/reset TIF_32BIT etc.
> + * Eventually we want to actually set the personality, but for now we
> + * should at least catch and tell the user what happened.
> + */
> +int restore_arch_thread(struct ckpt_ctx *ctx, struct ckpt_hdr_task *h)
> +{
> + int me = test_thread_flag(TIF_32BIT);
> + int ckpted = (!!(h->arch_flags & CKPT_ARCH_32BIT));
> +
> + /* all's we if both are 32-bit or 64-bit */
> + if (!(me ^ ckpted))
> + return 0;
> +
> + if (me)
> + ckpt_err(ctx, -EINVAL,
> + "32-bit task trying to restart a 64-bit one\n");
> + else
> + ckpt_err(ctx, -EINVAL,
> + "64-bit task trying to restart a 32-bit one\n");
> + return -EINVAL;
> +}
> +
> /* read the thread_struct into the current task */
> int restore_thread(struct ckpt_ctx *ctx)
> {
> diff --git a/arch/s390/mm/checkpoint.c b/arch/s390/mm/checkpoint.c
> index 40dd417..639df3f 100644
> --- a/arch/s390/mm/checkpoint.c
> +++ b/arch/s390/mm/checkpoint.c
> @@ -81,6 +81,10 @@ static void s390_mm(int op, struct ckpt_hdr_mm_context *h,
> CKPT_COPY(op, h->asce_limit, mm->context.asce_limit);
> }
>
> +/* called early to set TIF_31BIT etc */
> +void checkpoint_ach_thread(struct ckpt_hdr_task *h, struct task_struct *t)
> +{ }
> +
> int checkpoint_thread(struct ckpt_ctx *ctx, struct task_struct *t)
> {
> return 0;
> @@ -141,6 +145,12 @@ int checkpoint_mm_context(struct ckpt_ctx *ctx, struct mm_struct *mm)
> * Restart
> */
>
> +/* called early to check/reset TIF_31BIT etc */
> +int restore_arch_thread(struct ckpt_ctx *ctx, struct ckpt_hdr_task *h)
> +{
> + return 0;
> +}
> +
> int restore_thread(struct ckpt_ctx *ctx)
> {
> return 0;
> diff --git a/arch/x86/mm/checkpoint.c b/arch/x86/mm/checkpoint.c
> index 2752fdf..5a33dfd 100644
> --- a/arch/x86/mm/checkpoint.c
> +++ b/arch/x86/mm/checkpoint.c
> @@ -165,6 +165,10 @@ static int may_checkpoint_thread(struct ckpt_ctx *ctx, struct task_struct *t)
> return 0;
> }
>
> +/* called early to set TIF_32BIT etc */
> +void checkpoint_arch_thread(struct ckpt_hdr_task *h, struct task_struct *t)
> +{ }
> +
> /* dump the thread_struct of a given task */
> int checkpoint_thread(struct ckpt_ctx *ctx, struct task_struct *t)
> {
> @@ -399,6 +403,12 @@ int checkpoint_mm_context(struct ckpt_ctx *ctx, struct mm_struct *mm)
> * Restart
> */
>
> +/* called early to check/reset TIF_32BIT etc */
> +int restore_arch_thread(struct ckpt_ctx *ctx, struct ckpt_hdr_task *h)
> +{
> + return 0;
> +}
> +
> /* read the thread_struct into the current task */
> int restore_thread(struct ckpt_ctx *ctx)
> {
> diff --git a/checkpoint/process.c b/checkpoint/process.c
> index 4cce6f8..2ad79ee 100644
> --- a/checkpoint/process.c
> +++ b/checkpoint/process.c
> @@ -138,6 +138,8 @@ static int checkpoint_task_struct(struct ckpt_ctx *ctx, struct task_struct *t)
> h->exit_state = t->exit_state;
> h->exit_code = t->exit_code;
>
> + checkpoint_arch_thread(h, t);
> +
> if (t->exit_state) {
> /* zombie - skip remaining state */
> BUG_ON(t->exit_state != EXIT_ZOMBIE);
> @@ -504,6 +506,10 @@ static int restore_task_struct(struct ckpt_ctx *ctx)
> if (IS_ERR(h))
> return PTR_ERR(h);
>
> + ret = restore_arch_thread(ctx, h);
> + if (ret)
> + return ret;
> +
> ret = -EINVAL;
> if (h->state == TASK_DEAD) {
> if (h->exit_state != EXIT_ZOMBIE)
> diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
> index 550f6e8..343a166 100644
> --- a/include/linux/checkpoint.h
> +++ b/include/linux/checkpoint.h
> @@ -161,12 +161,18 @@ extern int restore_task(struct ckpt_ctx *ctx);
> extern int pre_restore_task(void);
> extern void post_restore_task(void);
>
> +/* arch_thread flags */
> +#define CKPT_ARCH_32BIT 0x01
> +
> /* arch hooks */
> +extern void checkpoint_arch_thread(struct ckpt_hdr_task *h,
> + struct task_struct *t);
> extern int checkpoint_write_header_arch(struct ckpt_ctx *ctx);
> extern int checkpoint_thread(struct ckpt_ctx *ctx, struct task_struct *t);
> extern int checkpoint_cpu(struct ckpt_ctx *ctx, struct task_struct *t);
> extern int checkpoint_mm_context(struct ckpt_ctx *ctx, struct mm_struct *mm);
>
> +extern int restore_arch_thread(struct ckpt_ctx *ctx, struct ckpt_hdr_task *h);
> extern int restore_read_header_arch(struct ckpt_ctx *ctx);
> extern int restore_thread(struct ckpt_ctx *ctx);
> extern int restore_cpu(struct ckpt_ctx *ctx);
> diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
> index 667b7aa..14976b2 100644
> --- a/include/linux/checkpoint_hdr.h
> +++ b/include/linux/checkpoint_hdr.h
> @@ -344,6 +344,7 @@ struct ckpt_hdr_task {
> __u32 compat_robust_futex_list; /* a compat __user ptr */
> __u32 robust_futex_head_len;
> __u64 robust_futex_list; /* a __user ptr */
> + __u64 arch_flags; /* includes ARCH_32BIT */
> } __attribute__((aligned(8)));
>
> /* Posix capabilities */
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