John David Anglin wrote:
>> Since many kernel versions I regularly faced reproducibly kernel hangs when
>> compiling some bigger files. The machine suddenly just seemed to hang.
>>
>> With spinlock debugging turned on I found this:
>>
>> BUG: spinlock recursion on CPU#0, tool/7263
>> lock: 10644000, .magic: dead4ead, .owner: tool/7263, .owner_cpu: 0
>> Backtrace:
>> [<10113a94>] show_stack+0x18/0x28
>>
>> BUG: spinlock lockup on CPU#0, tool/7263, 10644000
>> Backtrace:
>> [<10113a94>] show_stack+0x18/0x28
>>
>> BUG: soft lockup - CPU#0 stuck for 61s! [tool:7263]
>> IASQ: 00000000 00000000 IAOQ: 102d55dc 102d557c
>> IIR: 03c008b3 ISR: 00000000 IOR: 00000000
>> CPU: 0 CR30: 7d1a4000 CR31: 11111111
>> ORIG_R28: 00000000
>> IAOQ[0]: _raw_spin_lock+0x15c/0x1c0
>> IAOQ[1]: _raw_spin_lock+0xfc/0x1c0
>> RP(r2): _raw_spin_lock+0x18c/0x1c0
>> Backtrace:
>> [<102d560c>] _raw_spin_lock+0x18c/0x1c0
>>
>> Kernel panic - not syncing: softlockup: hung tasks
>> Backtrace:
>> [<10113a94>] show_stack+0x18/0x28
>
> I have tested the proposed change using 2.6.30-rc6 and a modified version
> of 2.6.22.10. I tested using SMP kernels running on a rp3440 and UP
> kernels on a c3750. I also tested changing the macros to just use
> preempt_disable/preempt_enable.
>
> The patch doesn't cause any new problems as far as I can tell.
That's good. Thanks for testing !
> However,
> it doesn't fix any of the problems that I currently see on these two
> machines. In particular, I see the occasional gcc testsuite timeout
> using SMP kernels. Programs that usually take a few seconds to run
> timeout after three minutes. These timeouts don't occur with UP kernels.
Ok, it fixes at least a kernel hang I faced regularily with my compilations...
> On the rp3440, the spinlock is definitely needed. With just
> preempt_disable/preempt_enable, a crash occurs during bootstrap
> at the point unused memory is recovered. Thus, the tlb purge
> issue referred to in the preceeding comment affects more than
> just N class.
>
> On the otherhand, it doesn't seem necessary to disable interrupts
> during the purge with UP kernels.
My kernel crashes happened with UP-kernels on a B2000 (1 CPU).
So, I still have the feeling that it's necessary to disable interrupts
on UP kernels as well.
The new cleaned-up attached patch below shows, that arch/parisc/kernel/pci-dma.c
is affected. My kernel crashes always happened when the machine was pretty
much loaded, during memory pressure when the system still wanted to load
something from disk.
In pci-dma.c the TLB flushing code is called from the DMA handlers, so
it does indicate that IRQ would need to be disabled.
One example I could imagine (with a UP-kernel):
- Process A runs some code, gets into kernel and executes clear_user_page() and locks
the pa_tlb_lock spinlock (inside the critical section).
- Suddenly Process B gets data from disk via DMA handlers in pci-dma.c
- DMA-Interrupt kicks in, the DMA handler tries to get the pa_tlb_lock and fails
since process A still holds the lock
-> machine deadlocks and kernel starts reporting about "hung tasks after 61seconds".
(just search the mailing list for such reports..)
So, even a UP-kernel is affected.
> With SMP kernels, it would be nice
> to know if the lockup was caused by an interruption during the tlb
> purge, or a preemption issue.
>
> I have the sense that disabling interrupts is wrong. That is any
> given CPU can only generate one PxTLB inter processor broadcast
> at a time. Disabling interrupts could cause a deadlock if a TLB
> purge was needed while the purge code was executing.
>
> The other alternative is to allow the processor that holds the lock
> to enter the flush code. This would fix the deadlock. Don't know how
> to code this (atomic compare and exchange?).
>
> The preempt_disable/preempt_enable crash on the rp3440 made me wonder
> if all tlb purge operations are properly protected with the tlb spinlock.
> I think we need to look at flush_tlb_all_local and copy_user_page_asm.
> They don't seem protected.
New patch attached.
Helge
diff --git a/arch/parisc/include/asm/tlbflush.h b/arch/parisc/include/asm/tlbflush.h
index 1f6fd4f..217588e 100644
--- a/arch/parisc/include/asm/tlbflush.h
+++ b/arch/parisc/include/asm/tlbflush.h
@@ -18,8 +18,8 @@
*/
extern spinlock_t pa_tlb_lock;
-#define purge_tlb_start(x) spin_lock(&pa_tlb_lock)
-#define purge_tlb_end(x) spin_unlock(&pa_tlb_lock)
+#define purge_tlb_start(flags) spin_lock_irqsave(&pa_tlb_lock, flags)
+#define purge_tlb_end(flags) spin_unlock_irqrestore(&pa_tlb_lock, flags)
extern void flush_tlb_all(void);
extern void flush_tlb_all_local(void *);
@@ -64,13 +64,14 @@ static inline void flush_tlb_page(struct vm_area_struct *vma,
unsigned long addr)
{
/* For one page, it's not worth testing the split_tlb variable */
+ unsigned long flags;
mb();
mtsp(vma->vm_mm->context,1);
- purge_tlb_start();
+ purge_tlb_start(flags);
pdtlb(addr);
pitlb(addr);
- purge_tlb_end();
+ purge_tlb_end(flags);
}
void __flush_tlb_range(unsigned long sid,
diff --git a/arch/parisc/kernel/cache.c b/arch/parisc/kernel/cache.c
index 837530e..e3c55f7 100644
--- a/arch/parisc/kernel/cache.c
+++ b/arch/parisc/kernel/cache.c
@@ -400,10 +400,11 @@ void clear_user_page_asm(void *page, unsigned long vaddr)
{
/* This function is implemented in assembly in pacache.S */
extern void __clear_user_page_asm(void *page, unsigned long vaddr);
+ unsigned long flags;
- purge_tlb_start();
+ purge_tlb_start(flags);
__clear_user_page_asm(page, vaddr);
- purge_tlb_end();
+ purge_tlb_end(flags);
}
#define FLUSH_THRESHOLD 0x80000 /* 0.5MB */
@@ -444,20 +445,22 @@ extern void clear_user_page_asm(void *page, unsigned long vaddr);
void clear_user_page(void *page, unsigned long vaddr, struct page *pg)
{
+ unsigned long flags;
purge_kernel_dcache_page((unsigned long)page);
- purge_tlb_start();
+ purge_tlb_start(flags);
pdtlb_kernel(page);
- purge_tlb_end();
+ purge_tlb_end(flags);
clear_user_page_asm(page, vaddr);
}
EXPORT_SYMBOL(clear_user_page);
void flush_kernel_dcache_page_addr(void *addr)
{
+ unsigned long flags;
flush_kernel_dcache_page_asm(addr);
- purge_tlb_start();
+ purge_tlb_start(flags);
pdtlb_kernel(addr);
- purge_tlb_end();
+ purge_tlb_end(flags);
}
EXPORT_SYMBOL(flush_kernel_dcache_page_addr);
@@ -490,8 +493,9 @@ void __flush_tlb_range(unsigned long sid, unsigned long start,
if (npages >= 512) /* 2MB of space: arbitrary, should be tuned */
flush_tlb_all();
else {
+ unsigned long flags;
mtsp(sid, 1);
- purge_tlb_start();
+ purge_tlb_start(flags);
if (split_tlb) {
while (npages--) {
pdtlb(start);
@@ -504,7 +508,7 @@ void __flush_tlb_range(unsigned long sid, unsigned long start,
start += PAGE_SIZE;
}
}
- purge_tlb_end();
+ purge_tlb_end(flags);
}
}
diff --git a/arch/parisc/kernel/pci-dma.c b/arch/parisc/kernel/pci-dma.c
index 7d927ea..b8ec5a0 100644
--- a/arch/parisc/kernel/pci-dma.c
+++ b/arch/parisc/kernel/pci-dma.c
@@ -90,12 +90,13 @@ static inline int map_pte_uncached(pte_t * pte,
if (end > PMD_SIZE)
end = PMD_SIZE;
do {
+ unsigned long flags;
if (!pte_none(*pte))
printk(KERN_ERR "map_pte_uncached: page already exists\n");
set_pte(pte, __mk_pte(*paddr_ptr, PAGE_KERNEL_UNC));
- purge_tlb_start();
+ purge_tlb_start(flags);
pdtlb_kernel(orig_vaddr);
- purge_tlb_end();
+ purge_tlb_end(flags);
vaddr += PAGE_SIZE;
orig_vaddr += PAGE_SIZE;
(*paddr_ptr) += PAGE_SIZE;
@@ -168,11 +169,12 @@ static inline void unmap_uncached_pte(pmd_t * pmd, unsigned long vaddr,
if (end > PMD_SIZE)
end = PMD_SIZE;
do {
+ unsigned long flags;
pte_t page = *pte;
pte_clear(&init_mm, vaddr, pte);
- purge_tlb_start();
+ purge_tlb_start(flags);
pdtlb_kernel(orig_vaddr);
- purge_tlb_end();
+ purge_tlb_end(flags);
vaddr += PAGE_SIZE;
orig_vaddr += PAGE_SIZE;
pte++;
--
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