Ok, I think I'm convinced ;)
Applied...
Serge E. Hallyn wrote:
> Quoting Serge E. Hallyn (serue@xxxxxxxxxx):
>> Well, perhaps I've been making this more complicated than it
>> needs to be.
>>
>> If we get frozen+checkpointed, then no matter whether we were
>> frozen with a real pending signal or not, we won't handle the
>> signal during restart, so we can treat it as though signr==0.
>>
>> So, in that case, the only thing we need to change at end of
>> sys_restart is to handle the case:
>>
>> /* Restart a different system call. */
>> if (retval == -ERESTART_RESTARTBLOCK
>> && regs->psw.addr == continue_addr) {
>> regs->gprs[2] = __NR_restart_syscall;
>> set_thread_flag(TIF_RESTART_SVC);
>> }
>>
>> Now that's of course a problem bc we don't know continue_addr
>> when we're in sys_restart(). So before we go into get_signal_to_deliver(),
>> we should set a new TIF flag which represents the fact that we are
>> inside do_signal with those conditions.
>>
>> Then at end of restore_thread(), if that flag is set, we do the
>>
>> regs->gprs[2] = __NR_restart_syscall;
>> set_thread_flag(TIF_RESTART_SVC);
>>
>> (which presumably goes into a helper)
>>
>> If there was a pending signal which we were intending to handle
>> when checkpointed, then that will simply be delivered after we
>> exit sys_restart. That is no different from the case where we
>> got another signal delivered while a slow sighandler was executing.
>>
>> I'll try implementing that idea.
>>
>> -serge
>
> Like so:
>
> From b50eb90da03e82ae6e7a2f1a8362e93c18d52074 Mon Sep 17 00:00:00 2001
> From: Serge E. Hallyn <serue@xxxxxxxxxx>
> Date: Thu, 11 Feb 2010 14:05:16 -0500
> Subject: [PATCH 1/1] set TIF_RESTART_SVC when needed after sys_restart
>
> Signed-off-by: Serge E. Hallyn <serue@xxxxxxxxxx>
> ---
> arch/s390/include/asm/checkpoint_hdr.h | 5 +++
> arch/s390/include/asm/thread_info.h | 2 +
> arch/s390/kernel/checkpoint.c | 52 +++++++++++++++++++++++++++++++-
> arch/s390/kernel/signal.c | 16 ++++++++++
> 4 files changed, 74 insertions(+), 1 deletions(-)
>
> diff --git a/arch/s390/include/asm/checkpoint_hdr.h b/arch/s390/include/asm/checkpoint_hdr.h
> index a8c2a3d..fd8be2a 100644
> --- a/arch/s390/include/asm/checkpoint_hdr.h
> +++ b/arch/s390/include/asm/checkpoint_hdr.h
> @@ -76,6 +76,11 @@ struct ckpt_hdr_cpu {
> __u8 instruction_fetch;
> };
>
> +struct ckpt_hdr_thread {
> + struct ckpt_hdr h;
> + __u64 thread_info_flags;
> +};
> +
> struct ckpt_hdr_mm_context {
> struct ckpt_hdr h;
> unsigned long vdso_base;
> diff --git a/arch/s390/include/asm/thread_info.h b/arch/s390/include/asm/thread_info.h
> index 66069e7..61e84e5 100644
> --- a/arch/s390/include/asm/thread_info.h
> +++ b/arch/s390/include/asm/thread_info.h
> @@ -99,6 +99,7 @@ static inline struct thread_info *current_thread_info(void)
> #define TIF_MEMDIE 18
> #define TIF_RESTORE_SIGMASK 19 /* restore signal mask in do_signal() */
> #define TIF_FREEZE 20 /* thread is freezing for suspend */
> +#define TIF_SIG_RESTARTBLOCK 23 /* restart must set TIF_RESTART_SVC */
>
> #define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME)
> #define _TIF_RESTORE_SIGMASK (1<<TIF_RESTORE_SIGMASK)
> @@ -114,6 +115,7 @@ static inline struct thread_info *current_thread_info(void)
> #define _TIF_POLLING_NRFLAG (1<<TIF_POLLING_NRFLAG)
> #define _TIF_31BIT (1<<TIF_31BIT)
> #define _TIF_FREEZE (1<<TIF_FREEZE)
> +#define _TIF_SIG_RESTARTBLOCK (1<<TIF_SIG_RESTARTBLOCK)
>
> #endif /* __KERNEL__ */
>
> diff --git a/arch/s390/kernel/checkpoint.c b/arch/s390/kernel/checkpoint.c
> index 60ba04d..cc7f341 100644
> --- a/arch/s390/kernel/checkpoint.c
> +++ b/arch/s390/kernel/checkpoint.c
> @@ -12,6 +12,7 @@
> #include <asm/system.h>
> #include <asm/pgtable.h>
> #include <asm/elf.h>
> +#include <asm/unistd.h>
>
> #include <linux/checkpoint.h>
> #include <linux/checkpoint_hdr.h>
> @@ -65,6 +66,18 @@ static void s390_copy_regs(int op, struct ckpt_hdr_cpu *h,
> BUG_ON(h->gprs[2] < 0);
> h->gprs[2] = 0;
> }
> +
> + /*
> + * if a checkpoint was taken while interrupted from a restartable
> + * syscall, then treat this as though signr==0 (since we did not
> + * handle the signal) and finish the last part of do_signal
> + */
> + if (op == CKPT_RST && test_thread_flag(TIF_SIG_RESTARTBLOCK)) {
> + regs->gprs[2] = __NR_restart_syscall;
> + set_thread_flag(TIF_RESTART_SVC);
> + clear_thread_flag(TIF_SIG_RESTARTBLOCK);
> + }
> +
> CKPT_COPY_ARRAY(op, h->fprs, thr->fp_regs.fprs, NUM_FPRS);
> CKPT_COPY_ARRAY(op, h->acrs, thr->acrs, NUM_ACRS);
> CKPT_COPY_ARRAY(op, h->per_control_regs,
> @@ -83,12 +96,24 @@ static void s390_mm(int op, struct ckpt_hdr_mm_context *h,
>
> int checkpoint_thread(struct ckpt_ctx *ctx, struct task_struct *t)
> {
> + struct ckpt_hdr_thread *h;
> + int ret;
> +
> /* we will eventually support this, as we do on x86-64 */
> if (test_tsk_thread_flag(t, TIF_31BIT)) {
> ckpt_err(ctx, -EINVAL, "checkpoint of 31-bit task\n");
> return -EINVAL;
> }
> - return 0;
> +
> + h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_THREAD);
> + if (!h)
> + return -ENOMEM;
> +
> + h->thread_info_flags = task_thread_info(t)->flags;
> + ret = ckpt_write_obj(ctx, &h->h);
> + ckpt_hdr_put(ctx, h);
> +
> + return ret;
> }
>
> /* dump the cpu state and registers of a given task */
> @@ -148,11 +173,36 @@ int checkpoint_mm_context(struct ckpt_ctx *ctx, struct mm_struct *mm)
>
> int restore_thread(struct ckpt_ctx *ctx)
> {
> + struct ckpt_hdr_thread *h;
> +
> /* a 31-bit task cannot call sys_restart right now */
> if (test_thread_flag(TIF_31BIT)) {
> ckpt_err(ctx, -EINVAL, "restart from 31-bit task\n");
> return -EINVAL;
> }
> +
> + h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_THREAD);
> + if (IS_ERR(h))
> + return PTR_ERR(h);
> +
> + /*
> + * If we were checkpointed while do_signal() interrupted a
> + * syscall with restart blocks, then we have some cleanup to
> + * do at end of restart, in order to finish our pretense of
> + * having handled signr==0. (See last part of do_signal).
> + *
> + * We can't set gprs[2] here bc we haven't copied registers
> + * yet, that happens later in restore_cpu(). So re-set the
> + * TIF_SIG_RESTARTBLOCK thread flag so we can detect it
> + * at restore_cpu()->s390_copy_regs() and do the right thing.
> + */
> + if (h->thread_info_flags & _TIF_SIG_RESTARTBLOCK)
> + set_thread_flag(TIF_SIG_RESTARTBLOCK);
> +
> + /* will have to handle TIF_RESTORE_SIGMASK as well */
> +
> + ckpt_hdr_put(ctx, h);
> +
> return 0;
> }
>
> diff --git a/arch/s390/kernel/signal.c b/arch/s390/kernel/signal.c
> index 1675c48..9b6ca21 100644
> --- a/arch/s390/kernel/signal.c
> +++ b/arch/s390/kernel/signal.c
> @@ -459,6 +459,16 @@ void do_signal(struct pt_regs *regs)
> break;
> case -ERESTART_RESTARTBLOCK:
> regs->gprs[2] = -EINTR;
> + /*
> + * This condition is the only one which requires
> + * special care after handling a signr==0. So if
> + * we get frozen and checkpointed at the
> + * get_signal_to_deliver() below, then we need
> + * to convey this condition to sys_restart() so it
> + * can set the restored thread up to run the restart
> + * block.
> + */
> + set_thread_flag(TIF_SIG_RESTARTBLOCK);
> }
> regs->svcnr = 0; /* Don't deal with this again. */
> }
> @@ -467,6 +477,12 @@ void do_signal(struct pt_regs *regs)
> the debugger may change all our registers ... */
> signr = get_signal_to_deliver(&info, &ka, regs, NULL);
>
> + /*
> + * we won't get frozen past this so clear the thread flag hinting
> + * to sys_restart that TIF_RESTART_SVC must be set.
> + */
> + clear_thread_flag(TIF_SIG_RESTARTBLOCK);
> +
> /* Depending on the signal settings we may need to revert the
> decision to restart the system call. */
> if (signr > 0 && regs->psw.addr == restart_addr) {
--
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