| Message ID | 1405069813-9270-1-git-send-email-sebastian.hesselbarth@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Jul 11, 2014 at 10:10:13AM +0100, Sebastian Hesselbarth wrote: > commit 431a84b1a4f7d1a0085d5b91330c5053cc8e8b12 > ("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: Indeed, I missed this part completely. > --- a/arch/arm/kernel/iwmmxt.S > +++ b/arch/arm/kernel/iwmmxt.S > @@ -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 > @@ -175,10 +181,6 @@ concan_load: > tmcr wCon, r2 > > 3: > -#ifdef CONFIG_PREEMPT_COUNT > - get_thread_info r10 > -#endif > -4: dec_preempt_count r10, r3 > mov pc, lr It looks fine to me. One optimisation you could do is to replace a couple of beq 3f with moveq pc, lr.
diff --git a/arch/arm/kernel/iwmmxt.S b/arch/arm/kernel/iwmmxt.S index a5599cf..fc95b89 100644 --- a/arch/arm/kernel/iwmmxt.S +++ b/arch/arm/kernel/iwmmxt.S @@ -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 @@ -175,10 +181,6 @@ concan_load: tmcr wCon, r2 3: -#ifdef CONFIG_PREEMPT_COUNT - get_thread_info r10 -#endif -4: dec_preempt_count r10, r3 mov pc, lr /*
commit 431a84b1a4f7d1a0085d5b91330c5053cc8e8b12 ("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(). Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com> Reported-by: Jean-Francois Moine <moinejf@free.fr> Fixes: 431a84b1a4f7 ("ARM: 8034/1: Disable preemption in iwmmxt_task_enable()") --- The offending commit was intoduced past v3.15-rc1 and the corresponding fix should also be queued up for stable v3.15+ Cc: Russell King <linux@arm.linux.org.uk> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Jean-Francois Moine <moinejf@free.fr> Cc: Jason Cooper <jason@lakedaemon.net> Cc: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org --- arch/arm/kernel/iwmmxt.S | 16 +++++++++------- 1 files changed, 9 insertions(+), 7 deletions(-)