Hi Sebastian,

On 01/13/2016 10:14 PM, Grygorii Strashko wrote:

On 01/13/2016 01:41 PM, Grygorii Strashko wrote:

quoted

On 01/12/2016 07:15 PM, Sebastian Andrzej Siewior wrote:

quoted

* Grygorii Strashko | 2015-12-28 20:00:09 [+0200]:

quoted

3) Seems there are some problem with HIGHMEM :(. System crashes if I'm trying
     to run hackbench (see log 1). I can run hackbench only if HIGHMEM is disabled.
     I've also tried to disable CONFIG_CPU_SW_DOMAIN_PAN, CONFIG_ARM_PATCH_PHYS_VIRT,
     and CONFIG_CPUSETS, before disabling HIGHMEM.
     Sorry, I'll not able to investigate it further because of Christmas holidays here.

I see. It seems not to trigger anything on x86.

Yah. I saw other reports - it seems this issue is not triggered on ARM SMP also
(as per report from Tim Sander). Will try to dig deeper.

I did more tests, but still don't know what is wrong.
1) vanilla 4.4 - no issue
2) 4.4-rt: CONFIG_PREEMPT_RT_BASE=n and CONFIG_PREEMPT_RT_FULL=n -- no issue
3) 4.4-rt: CONFIG_DEBUG_HIGHMEM=y -- issue is present log1
4) 4.4-rt: this is interesting ;)
I can run hackbench few times without issues If I run hackbench with RT priority (log2)
But I got crash immediately once I run it using non-RT priorities.

Seems I've found root cause of the issue - FIX_KMAP_BEGIN offset need to be taken into
account in switch_kmaps() and below diff fixes this issue for me.
What I'm not fully understand is why I'm the only one who hit this issue :(
New functionality was added by commit:
commit a5f4c561b3b19a9bc43a81da6382b0098ebbc1fb
    ARM: 8415/1: early fixmap support for earlycon

and it is enabled by default.

Luckiness :(

diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c
index deabc36..b9b4f9c 100644
--- a/arch/arm/mm/highmem.c
+++ b/arch/arm/mm/highmem.c

@@ -167,7 +167,7 @@ void switch_kmaps(struct task_struct *prev_p, struct task_struct *next_p)
         * Clear @prev's kmap_atomic mappings
         */
        for (i = 0; i < prev_p->kmap_idx; i++) {
-               int idx = i + KM_TYPE_NR * smp_processor_id();
+               int idx = FIX_KMAP_BEGIN + i + KM_TYPE_NR * smp_processor_id();
 
                set_fixmap_pte(idx, __pte(0));
        }

@@ -175,7 +175,7 @@ void switch_kmaps(struct task_struct *prev_p, struct task_struct *next_p)
         * Restore @next_p's kmap_atomic mappings
         */
        for (i = 0; i < next_p->kmap_idx; i++) {
-               int idx = i + KM_TYPE_NR * smp_processor_id();
+               int idx = FIX_KMAP_BEGIN + i + KM_TYPE_NR * smp_processor_id();
 
                if (!pte_none(next_p->kmap_pte[i]))
                        set_fixmap_pte(idx, next_p->kmap_pte[i]);

-- 
regards,
-grygorii