Commit 8cf2389b authored Jul 14, 2014 by Sebastian Hesselbarth Committed by Russell King Jul 18, 2014

ARM: 8100/1: Fix preemption disable in iwmmxt_task_enable()



commit 431a84b1
 ("ARM: 8034/1: Disable preemption in iwmmxt_task_enable()")
introduced macros {inc,dec}_preempt_count to iwmmxt_task_enable
to make it run with preemption disabled.

Unfortunately, other functions in iwmmxt.S also use concan_{save,dump,load}
sections located in iwmmxt_task_enable() to deal with iWMMXt coprocessor.
This causes an unbalanced preempt_count due to excessive dec_preempt_count
and destroyed return addresses in callers of concan_ labels due to a register
collision:

Linux version 3.16.0-rc3-00062-gd92a333-dirty (jef@armhf) (gcc version 4.8.3 (Debian 4.8.3-4) ) #5 PREEMPT Thu Jul 3 19:46:39 CEST 2014
CPU: ARMv7 Processor [560f5815] revision 5 (ARMv7), cr=10c5387d
CPU: PIPT / VIPT nonaliasing data cache, PIPT instruction cache
Machine model: SolidRun CuBox
...
PJ4 iWMMXt v2 coprocessor enabled.
...
Unable to handle kernel paging request at virtual address fffffffe
pgd = bb25c000
[fffffffe] *pgd=3bfde821, *pte=00000000, *ppte=00000000
Internal error: Oops: 80000007 [#1] PREEMPT ARM
Modules linked in:
CPU: 0 PID: 62 Comm: startpar Not tainted 3.16.0-rc3-00062-gd92a333-dirty #5
task: bb230b80 ti: bb256000 task.ti: bb256000
PC is at 0xfffffffe
LR is at iwmmxt_task_copy+0x44/0x4c
pc : [<fffffffe>]    lr : [<800130ac>]    psr: 40000033
sp : bb257de8  ip : 00000013  fp : bb257ea4
r10: bb256000  r9 : fffffdfe  r8 : 76e898e6
r7 : bb257ec8  r6 : bb256000  r5 : 7ea12760  r4 : 000000a0
r3 : ffffffff  r2 : 00000003  r1 : bb257df8  r0 : 00000000
Flags: nZcv  IRQs on  FIQs on  Mode SVC_32  ISA Thumb  Segment user
Control: 10c5387d  Table: 3b25c019  DAC: 00000015
Process startpar (pid: 62, stack limit = 0xbb256248)

This patch fixes the issue by moving concan_{save,dump,load} into separate
code sections and make iwmmxt_task_enable() call them in the same way the
other functions use concan_ symbols. The test for valid ownership is moved
to concan_save and is safe for the other user of it, iwmmxt_task_disable().
The register collision is also resolved by moving concan_ symbols as
{inc,dec}_preempt_count are now local to iwmmxt_task_enable().

Fixes: 431a84b1 ("ARM: 8034/1: Disable preemption in iwmmxt_task_enable()")

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

parent 6b076991

arch/arm/kernel/iwmmxt.S

+12 −11

Original line number	Diff line number	Diff line
		@@ -94,13 +94,19 @@ ENTRY(iwmmxt_task_enable)

		mrc p15, 0, r2, c2, c0, 0
		mov r2, r2 @ cpwait
		bl concan_save

		teq r1, #0 @ test for last ownership
		mov lr, r9 @ normal exit from exception
		beq concan_load @ no owner, skip save
		#ifdef CONFIG_PREEMPT_COUNT
		get_thread_info r10
		#endif
		4: dec_preempt_count r10, r3
		mov pc, r9 @ normal exit from exception

		concan_save:

		teq r1, #0 @ test for last ownership
		beq concan_load @ no owner, skip save

		tmrc r2, wCon

		@ CUP? wCx
		@@ -138,7 +144,7 @@ concan_dump:
		wstrd wR15, [r1, #MMX_WR15]

		2: teq r0, #0 @ anything to load?
		beq 3f
		moveq pc, lr @ if not, return

		concan_load:

		@@ -171,14 +177,9 @@ concan_load:
		@ clear CUP/MUP (only if r1 != 0)
		teq r1, #0
		mov r2, #0
		beq 3f
		tmcr wCon, r2
		moveq pc, lr

		3:
		#ifdef CONFIG_PREEMPT_COUNT
		get_thread_info r10
		#endif
		4: dec_preempt_count r10, r3
		tmcr wCon, r2
		mov pc, lr

		/*