I had a user report a problem where the /proc/self/stat field 28 is now
zero where it used to be a value that could be used to determine the
stack location. The following illustrates the problem:
cut -f1,2,28,29 -d\ /proc/[1-9]*/stat | grep -v " 0 0" | grep " 0 "
Commit d899bf7b55f changed the copy_process in kernel/fork.c to
expect a useful stack_start value. I contemplated either using the
current->mm->start_stack or the ar_bspstore value. Turns out the
ar_bspstore value appears to more nearly meet the above commit's intent.
That said, the above commit has been partially reverted.
I worked around the problem by passing stack_start with a valid value,
but setting stack_size to 0. copy_thread can then key off that changed
value to retain its old behavior.
I have modified sys_clone, but I have not verified the values. The code
path gets traversed, but none of the tasks calling sys_clone showed up
in the old trace so I have not verified the values are consistent.
Signed-off-by: Robin Holt <holt@xxxxxxx>
To: linux-ia64@xxxxxxxxxxxxxxx
Cc: Jack Steiner <steiner@xxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Stefani Seibold <stefani@xxxxxxxxxxx>
---
arch/ia64/kernel/entry.S | 8 ++++++++
arch/ia64/kernel/process.c | 2 +-
2 files changed, 9 insertions(+), 1 deletion(-)
Index: ia64_stack_start_V1/arch/ia64/kernel/entry.S
===================================================================
--- ia64_stack_start_V1.orig/arch/ia64/kernel/entry.S 2010-04-25 06:45:22.406898052 -0500
+++ ia64_stack_start_V1/arch/ia64/kernel/entry.S 2010-04-25 06:53:45.575399384 -0500
@@ -114,15 +114,19 @@ GLOBAL_ENTRY(sys_clone2)
alloc r16=ar.pfs,8,2,6,0
DO_SAVE_SWITCH_STACK
adds r2=PT(R16)+IA64_SWITCH_STACK_SIZE+16,sp
+ adds r3=PT(AR_BSPSTORE)+IA64_SWITCH_STACK_SIZE+16,sp
mov loc0=rp
mov loc1=r16 // save ar.pfs across do_fork
.body
mov out1=in1
mov out3=in2
tbit.nz p6,p0=in0,CLONE_SETTLS_BIT
+ cmp.eq p7,p0=in1,r0
mov out4=in3 // parent_tidptr: valid only w/CLONE_PARENT_SETTID
;;
(p6) st8 [r2]=in5 // store TLS in r16 for copy_thread()
+(p7) ld8 out1=[r3] // stack_start: kernel expects a valid value
+(p7) mov out3=r0
mov out5=in4 // child_tidptr: valid only w/CLONE_CHILD_SETTID or CLONE_CHILD_CLEARTID
adds out2=IA64_SWITCH_STACK_SIZE+16,sp // out2 = ®s
mov out0=in0 // out0 = clone_flags
@@ -146,15 +150,19 @@ GLOBAL_ENTRY(sys_clone)
alloc r16=ar.pfs,8,2,6,0
DO_SAVE_SWITCH_STACK
adds r2=PT(R16)+IA64_SWITCH_STACK_SIZE+16,sp
+ adds r3=PT(AR_BSPSTORE)+IA64_SWITCH_STACK_SIZE+16,sp
mov loc0=rp
mov loc1=r16 // save ar.pfs across do_fork
.body
mov out1=in1
mov out3=16 // stacksize (compensates for 16-byte scratch area)
tbit.nz p6,p0=in0,CLONE_SETTLS_BIT
+ cmp.eq p7,p0=in1,r0
mov out4=in2 // parent_tidptr: valid only w/CLONE_PARENT_SETTID
;;
(p6) st8 [r2]=in4 // store TLS in r13 (tp)
+(p7) ld8 out1=[r3] // stack_start: kernel expects a valid value
+(p7) mov out3=r0
mov out5=in3 // child_tidptr: valid only w/CLONE_CHILD_SETTID or CLONE_CHILD_CLEARTID
adds out2=IA64_SWITCH_STACK_SIZE+16,sp // out2 = ®s
mov out0=in0 // out0 = clone_flags
Index: ia64_stack_start_V1/arch/ia64/kernel/process.c
===================================================================
--- ia64_stack_start_V1.orig/arch/ia64/kernel/process.c 2010-04-25 06:45:22.438977238 -0500
+++ ia64_stack_start_V1/arch/ia64/kernel/process.c 2010-04-25 06:48:03.671076650 -0500
@@ -452,7 +452,7 @@ copy_thread(unsigned long clone_flags,
if (likely(user_mode(child_ptregs))) {
if (clone_flags & CLONE_SETTLS)
child_ptregs->r13 = regs->r16; /* see sys_clone2() in entry.S */
- if (user_stack_base) {
+ if (user_stack_base && user_stack_size) {
child_ptregs->r12 = user_stack_base + user_stack_size - 16;
child_ptregs->ar_bspstore = user_stack_base;
child_ptregs->ar_rnat = 0;
--
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