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Date: Mon, 20 Jul 2015 10:20:04 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Heiko Carstens <heiko.carstens@...ibm.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
"H. Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>, Dave Hansen <dave@...1.net>,
Andrew Morton <akpm@...ux-foundation.org>,
Oleg Nesterov <oleg@...hat.com>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: [PATCH] s390, sched: Fix thread_struct move fallout to __switch_to()
* Heiko Carstens <heiko.carstens@...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
--
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