[PATCH] s390, sched: Fix thread_struct move fallout to __switch_to()

[Ingo Molnar <mingo@kernel.org>]

* Heiko Carstens <heiko.carstens@de.ibm.com> wrote:

> Unfortunately not true. It breaks the build on s390 since a couple of
> displacements used in asm code now get too large:
> 
> arch/s390/kernel/entry.S:181: Error: operand out of range (0x00000000000018a8 is not between 0x0000000000000000 and 0x0000000000000fff)
> arch/s390/kernel/entry.S:191: Error: operand out of range (0x00000000000018a8 is not between 0x0000000000000000 and 0x0000000000000fff)
> arch/s390/kernel/entry.S:423: Error: operand out of range (0x0000000000001924 is not between 0x0000000000000000 and 0x0000000000000fff)
> arch/s390/kernel/entry.S:437: Error: operand out of range (0x00000000000018e8 is not between 0x0000000000000000 and 0x0000000000000fff)
> arch/s390/kernel/entry.S:438: Error: operand out of range (0x00000000000018e0 is not between 0x0000000000000000 and 0x0000000000000fff)
> arch/s390/kernel/entry.S:439: Error: operand out of range (0x00000000000018f0 is not between 0x0000000000000000 and 0x0000000000000fff)
> make[1]: *** [arch/s390/kernel/entry.o] Error 1
> 
> Let's see how we can fix this.

Sorry about this!

So I looked at the __switch_to() assembly, and the main complication appears to be 
that we have two uses of 'prev':

        lg      %r4,__THREAD_info(%r2)          # get thread_info of prev


        stg     %r15,__THREAD_ksp(%r2)          # store kernel stack of prev

the __THREAD_info offset is best expressed relative to task_struct - the 
__THREAD_ksp offset is best expressed relative to thread_struct.

I.e. I think the best fix would be to extend the signature of s390's __switch_to() 
from (prev,next) to (prev,next,prev_thread,next_thread).

Is the C parameter mapping r2,r3,r4,r5? If yes then the patch below should do the 
trick. (Utterly untested.)

Note:

  - I renamed __THREAD_info to __TASK_thread_info, to better separate task_struct
    and thread_struct offsets syntactically and visually.

  - I removed __THREAD_mm_segment which is unused

I also looked at fixing pgm_check_handler(), but my s390-fu gave up completely on 
that one: task_struct is in 'r14', but this is a hardware entry function it 
appears. So to fix it we'd have to pick a temporary register, put thread_struct 
pointer into it, and fix up these offsets:

arch/s390/kernel/asm-offsets.c: DEFINE(__THREAD_per_address, offsetof(struct task_struct, thread.per_event.address));
arch/s390/kernel/asm-offsets.c: DEFINE(__THREAD_per_paid, offsetof(struct task_struct, thread.per_event.paid));
arch/s390/kernel/asm-offsets.c: DEFINE(__THREAD_trap_tdb, offsetof(struct task_struct, thread.trap_tdb));

to be thread_struct relative.

Thanks,

	Ingo

==============>

 arch/s390/include/asm/switch_to.h |  7 +++++--
 arch/s390/kernel/asm-offsets.c    |  5 ++---
 arch/s390/kernel/entry.S          | 14 +++++++++-----
 3 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/arch/s390/include/asm/switch_to.h b/arch/s390/include/asm/switch_to.h
index d62e7a69605f..aa854b600938 100644
--- a/arch/s390/include/asm/switch_to.h
+++ b/arch/s390/include/asm/switch_to.h
@@ -10,7 +10,10 @@
 #include <linux/thread_info.h>
 #include <asm/ptrace.h>
 
-extern struct task_struct *__switch_to(void *, void *);
+extern struct task_struct *
+__switch_to(struct task_struct *prev, struct task_struct *next,
+	    struct thread_struct *prev_thread, struct thread_struct *next_thrad);
+
 extern void update_cr_regs(struct task_struct *task);
 
 static inline int test_fp_ctl(u32 fpc)
@@ -169,7 +172,7 @@ static inline void restore_access_regs(unsigned int *acrs)
 		restore_access_regs(&next->thread.acrs[0]);		\
 		restore_ri_cb(next->thread.ri_cb, prev->thread.ri_cb);	\
 	}								\
-	prev = __switch_to(prev,next);					\
+	prev = __switch_to(prev, next, &prev->thread, &next->thread);	\
 } while (0)
 
 #endif /* __ASM_SWITCH_TO_H */
diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
index c7d1b9d09011..2b422297660f 100644
--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -23,9 +23,8 @@
 
 int main(void)
 {
-	DEFINE(__THREAD_info, offsetof(struct task_struct, stack));
-	DEFINE(__THREAD_ksp, offsetof(struct task_struct, thread.ksp));
-	DEFINE(__THREAD_mm_segment, offsetof(struct task_struct, thread.mm_segment));
+	DEFINE(__TASK_thread_info, offsetof(struct task_struct, stack));
+	DEFINE(__THREAD_ksp, offsetof(struct thread_struct, ksp));
 	BLANK();
 	DEFINE(__TASK_pid, offsetof(struct task_struct, pid));
 	BLANK();
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 3238893c9d4f..c2fcb9e7ad25 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -170,17 +170,21 @@ _PIF_WORK	= (_PIF_PER_TRAP)
 	.section .kprobes.text, "ax"
 
 /*
- * Scheduler resume function, called by switch_to
+ * Low level scheduler resume function, called by switch_to():
+ *
  *  gpr2 = (task_struct *) prev
  *  gpr3 = (task_struct *) next
+ *  gpr4 = (thread_struct *) prev->thread
+ *  gpr5 = (thread_struct *) next->thread
+ *
  * Returns:
  *  gpr2 = prev
  */
 ENTRY(__switch_to)
 	stmg	%r6,%r15,__SF_GPRS(%r15)	# store gprs of prev task
-	stg	%r15,__THREAD_ksp(%r2)		# store kernel stack of prev
-	lg	%r4,__THREAD_info(%r2)		# get thread_info of prev
-	lg	%r5,__THREAD_info(%r3)		# get thread_info of next
+	stg	%r15,__THREAD_ksp(%r4)		# store kernel stack of prev
+	lg	%r4,__TASK_thread_info(%r2)	# get thread_info of prev
+	lg	%r5,__TASK_thread_info(%r3)	# get thread_info of next
 	lgr	%r15,%r5
 	aghi	%r15,STACK_INIT			# end of kernel stack of next
 	stg	%r3,__LC_CURRENT		# store task struct of next
@@ -188,7 +192,7 @@ ENTRY(__switch_to)
 	stg	%r15,__LC_KERNEL_STACK		# store end of kernel stack
 	lctl	%c4,%c4,__TASK_pid(%r3)		# load pid to control reg. 4
 	mvc	__LC_CURRENT_PID+4(4,%r0),__TASK_pid(%r3) # store pid of next
-	lg	%r15,__THREAD_ksp(%r3)		# load kernel stack of next
+	lg	%r15,__THREAD_ksp(%r5)		# load kernel stack of next
 	lmg	%r6,%r15,__SF_GPRS(%r15)	# load gprs of next task
 	br	%r14