Re: [BUG] kernel BUG at arch/i386/mm/highmem.c:15! on 2.6.23-rc8/rc9

[gurudas pai <gurudas.pai@oracle.com>]

Hugh Dickins wrote:
> On Thu, 4 Oct 2007, gurudas pai wrote:
>> Nick Piggin wrote:
>>>>> While running Oracle database test on x86/6GB RAM machine panics with
>>>>> following messages.
>>>> Hmm, seems like something in sys_remap_file_pages might have broken.
>>>> It's a bit hard to work out from the backtrace, though.
>>>>
>>>> Is it possible you can strace to find the arguments for the
>>>> remap_file_pages that goes wrong?
>>> Ahh, I think it's just underflowing the preempt count somewhere, which
>>> is leading highmem.c:15 to just *think* it is in an interrupt.
>>>
>>> But you aren't running a preemptible kernel, which makes it unusual...
>>> it would have to be coming from interrupt code (or just random corruption).
>>> Still, preempt debugging should catch those cases as well.
>>>
>>> So, can you disregard my last message, and instead compile a kernel
>>> with CONFIG_PREEMPT and CONFIG_DEBUG_PREEMPT, and see what
>>> messages come up?
>> With CONFIG_PREEMPT and CONFIG_DEBUG_PREEMPT set I got following messages on
>> rc9.
>>
>> BUG: using smp_processor_id() in preemptible [00000001] code: oracle/3631
>> caller is kunmap_atomic+0xb/0x82
>>  [<c04ec241>] debug_smp_processor_id+0xa1/0xb4
>>  [<c0420dd0>] kunmap_atomic+0xb/0x82
>>  [<c045fae3>] __do_fault+0x55/0x35b
>>  [<c04623e8>] handle_mm_fault+0x4d0/0x909
>>  [<c0460624>] follow_page+0x1d9/0x228
>>  [<c0462a71>] get_user_pages+0x250/0x332
>>  [<c0462bce>] make_pages_present+0x7b/0x90
>>  [<c045f06a>] sys_remap_file_pages+0x2de/0x330
>>  [<c0404f0e>] syscall_call+0x7/0xb
>>  [<c0620000>] ioctl_standard_call+0x209/0x2ce
> 
> Very helpful, thanks.  Guru, please try the appended patch, I think
> you'll find it fixes it for you (it did for me, once I'd puzzled out
> why I was failing to reproduce the problem - tests on ext3 don't work).
> Thank you so much for reporting this just in time!
> 
> 
> [PATCH] fix sys_remap_file_pages BUG at highmem.c:15!
> 
> Gurudas Pai reports kernel BUG at arch/i386/mm/highmem.c:15! below
> sys_remap_file_pages, while running Oracle database test on x86 in 6GB RAM:
> kunmap thinks we're in_interrupt because the preempt count has wrapped.
> 
> That's because __do_fault expected to unmap page_table, but one of its two
> callers do_nonlinear_fault already unmapped it: let do_linear_fault unmap
> it first too, and then there's no need to pass the page_table arg down.
> 
> Why have we been so slow to notice this?  Probably through forgetting
> that the mapping_cap_account_dirty test means that sys_remap_file_pages
> nowadays only goes the full nonlinear vma route on a few memory-backed
> filesystems like ramfs, tmpfs and hugetlbfs.
> 
> Signed-off-by: Hugh Dickins <hugh@veritas.com>
> 
> --- 2.6.23-rc9/mm/memory.c	2007-07-26 19:49:58.000000000 +0100
> +++ linux/mm/memory.c	2007-10-04 15:42:20.000000000 +0100
> @@ -2307,13 +2307,14 @@ oom:
>   * do not need to flush old virtual caches or the TLB.
>   *
>   * We enter with non-exclusive mmap_sem (to exclude vma changes,
> - * but allow concurrent faults), and pte mapped but not yet locked.
> + * but allow concurrent faults), and pte neither mapped nor locked.
>   * We return with mmap_sem still held, but pte unmapped and unlocked.
>   */
>  static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> -		unsigned long address, pte_t *page_table, pmd_t *pmd,
> +		unsigned long address, pmd_t *pmd,
>  		pgoff_t pgoff, unsigned int flags, pte_t orig_pte)
>  {
> +	pte_t *page_table;
>  	spinlock_t *ptl;
>  	struct page *page;
>  	pte_t entry;
> @@ -2327,7 +2328,6 @@ static int __do_fault(struct mm_struct *
>  	vmf.flags = flags;
>  	vmf.page = NULL;
>  
> -	pte_unmap(page_table);
>  	BUG_ON(vma->vm_flags & VM_PFNMAP);
>  
>  	if (likely(vma->vm_ops->fault)) {
> @@ -2468,8 +2468,8 @@ static int do_linear_fault(struct mm_str
>  			- vma->vm_start) >> PAGE_CACHE_SHIFT) + vma->vm_pgoff;
>  	unsigned int flags = (write_access ? FAULT_FLAG_WRITE : 0);
>  
> -	return __do_fault(mm, vma, address, page_table, pmd, pgoff,
> -							flags, orig_pte);
> +	pte_unmap(page_table);
> +	return __do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
>  }
>  
>  
> @@ -2552,9 +2552,7 @@ static int do_nonlinear_fault(struct mm_
>  	}
>  
>  	pgoff = pte_to_pgoff(orig_pte);
> -
> -	return __do_fault(mm, vma, address, page_table, pmd, pgoff,
> -							flags, orig_pte);
> +	return __do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
>  }
>  
>  /*

Yes, indeed this patch worked for me , test completed successfully!! (on 
preempt kernel). Will continue testing with non-preempt kernel and 
update you if I hit any issue.

Thank you all for your time and effort.

Regards,
-Guru