[CRIU] [PATCH 1/8] signals: dump alternate stack as misc parameters

[Andrey Wagin]

2013/7/11 Andrey Wagin <avagin at gmail.com>:
> 2013/7/11 Pavel Emelyanov <xemul at parallels.com>:
>> On 07/11/2013 01:46 PM, Andrey Vagin wrote:
>>> The initilization stage is not good for that, because it can fail.
>>
>> IMO it should be done as early as possible, as the sas info is to
>> be used by sigreturn rescue from parasite.
>
> Yes, you are rigth. I forgot about this. Thanks.

I was thinking a bit more and changed my mind.

If sas is NULL in sigframe, it will not changed by sigreturn. parasite
doesn't change sas, so this patch is correct.

Currently sigframe is generated before executing a parasite. We should
to do minimum actions before entering in daemon mode, because only
here parasite can rollback itself.

>
>>
>>> Signed-off-by: Andrey Vagin <avagin at openvz.org>
>>> ---
>>>  cr-dump.c          |  3 +++
>>>  include/parasite.h | 10 +++++++++-
>>>  parasite-syscall.c | 10 ----------
>>>  pie/parasite.c     |  8 ++++----
>>>  4 files changed, 16 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/cr-dump.c b/cr-dump.c
>>> index ceee96f..9a7d756 100644
>>> --- a/cr-dump.c
>>> +++ b/cr-dump.c
>>> @@ -668,6 +668,9 @@ static int dump_task_core_all(struct parasite_ctl *ctl,
>>>       core_put_tls(core, misc->tls);
>>>       CORE_THREAD_ARCH_INFO(core)->clear_tid_addr = encode_pointer(misc->tid_addr);
>>>
>>> +     BUG_ON(!core->thread_core->sas);
>>> +     copy_sas(core->thread_core->sas, &misc->sas);
>>> +
>>>       ret = pb_write_one(fd_core, core, PB_CORE);
>>>       if (ret < 0)
>>>               goto err;
>>> diff --git a/include/parasite.h b/include/parasite.h
>>> index 0fbdd2c..334e31d 100644
>>> --- a/include/parasite.h
>>> +++ b/include/parasite.h
>>> @@ -71,7 +71,6 @@ struct parasite_init_args {
>>>       k_rtsigset_t            sig_blocked;
>>>
>>>       struct rt_sigframe      *sigframe;
>>> -     stack_t                 sas;
>>>  };
>>>
>>>  struct parasite_log_args {
>>> @@ -150,6 +149,8 @@ struct parasite_dump_misc {
>>>       u32 pgid;
>>>       u32 tls;
>>>       u32 umask;
>>> +
>>> +     stack_t                 sas;
>>>  };
>>>
>>>  #define PARASITE_MAX_GROUPS  (PAGE_SIZE / sizeof(unsigned int) - 2 * sizeof(unsigned))
>>> @@ -168,6 +169,13 @@ struct parasite_dump_thread {
>>>       stack_t                 sas;
>>>  };
>>>
>>> +static inline void copy_sas(ThreadSasEntry *dst, const stack_t *src)
>>> +{
>>> +     dst->ss_sp = encode_pointer(src->ss_sp);
>>> +     dst->ss_size = (u64)src->ss_size;
>>> +     dst->ss_flags = src->ss_flags;
>>> +}
>>> +
>>>  #define PARASITE_MAX_FDS     (PAGE_SIZE / sizeof(int))
>>>
>>>  struct parasite_drain_fd {
>>> diff --git a/parasite-syscall.c b/parasite-syscall.c
>>> index 2ca90f6..79dc7cd 100644
>>> --- a/parasite-syscall.c
>>> +++ b/parasite-syscall.c
>>> @@ -370,13 +370,6 @@ static int parasite_set_logfd(struct parasite_ctl *ctl, pid_t pid)
>>>       return 0;
>>>  }
>>>
>>> -static void copy_sas(ThreadSasEntry *dst, stack_t *src)
>>> -{
>>> -     dst->ss_sp = encode_pointer(src->ss_sp);
>>> -     dst->ss_size = (u64)src->ss_size;
>>> -     dst->ss_flags = src->ss_flags;
>>> -}
>>> -
>>>  static int parasite_init(struct parasite_ctl *ctl, pid_t pid, struct pstree_item *item)
>>>  {
>>>       static int ssock = -1;
>>> @@ -428,9 +421,6 @@ static int parasite_init(struct parasite_ctl *ctl, pid_t pid, struct pstree_item
>>>       ctl->sig_blocked = args->sig_blocked;
>>>       ctl->use_sig_blocked = true;
>>>
>>> -     BUG_ON(!item->core[0]->thread_core->sas);
>>> -     copy_sas(item->core[0]->thread_core->sas, &args->sas);
>>> -
>>>       sock = accept(ssock, NULL, 0);
>>>       if (sock < 0) {
>>>               pr_perror("Can't accept connection to the transport socket");
>>> diff --git a/pie/parasite.c b/pie/parasite.c
>>> index 125305e..eb5186d 100644
>>> --- a/pie/parasite.c
>>> +++ b/pie/parasite.c
>>> @@ -149,6 +149,10 @@ static int dump_misc(struct parasite_dump_misc *args)
>>>       args->umask = sys_umask(0);
>>>       sys_umask(args->umask); /* never fails */
>>>
>>> +     ret = sys_sigaltstack(NULL, &args->sas);
>>> +     if (ret)
>>> +             return ret;
>>> +
>>>       ret = sys_prctl(PR_GET_TID_ADDRESS, (unsigned long) &args->tid_addr, 0, 0, 0);
>>>
>>>       return ret;
>>> @@ -250,10 +254,6 @@ static int init(struct parasite_init_args *args)
>>>       if (ret)
>>>               return -1;
>>>
>>> -     ret = sys_sigaltstack(NULL, &args->sas);
>>> -     if (ret)
>>> -             goto err;
>>> -
>>>       tsock = sys_socket(PF_UNIX, SOCK_STREAM, 0);
>>>       if (tsock < 0) {
>>>               ret = tsock;
>>>
>>
>>