Hi,
On Sunday 20 April 2014 07:56 AM, Davidlohr Bueso wrote:
> Performing vma lookups without taking the mm->mmap_sem is asking
> for trouble. While doing the search, the vma in question can be
> modified or even removed before returning to the caller. Take the
> lock (shared) in order to avoid races while iterating through
> the vmacache and/or rbtree.
>
> This patch is completely *untested*.
>
> Signed-off-by: Davidlohr Bueso <davidlohr@xxxxxx>
> Cc: Vineet Gupta <vgupta@xxxxxxxxxxxx>
> ---
> arch/arc/kernel/troubleshoot.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arc/kernel/troubleshoot.c b/arch/arc/kernel/troubleshoot.c
> index 73a7450..3a5a5c1 100644
> --- a/arch/arc/kernel/troubleshoot.c
> +++ b/arch/arc/kernel/troubleshoot.c
> @@ -90,7 +90,7 @@ static void show_faulting_vma(unsigned long address, char *buf)
> /* can't use print_vma_addr() yet as it doesn't check for
> * non-inclusive vma
> */
> -
> + down_read(¤t->active_mm->mmap_sem);
Actually avoiding the lock here was intentional - atleast in the past, in case of
a crash from mmap_region() - due to our custom mmap syscall handler (not in
mainline) it would cause a double lockup.
However given that this code is now only called for user contexts [if
user_mode(regs)] above becomes moot point anyways and it would be safe to do that.
So, yes this looks good.
A minor suggestion though - can you please use a tmp for current->active_mm as
there are 3 users now in the function.
Acked-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>
Thx
-Vineet
> vma = find_vma(current->active_mm, address);
>
> /* check against the find_vma( ) behaviour which returns the next VMA
> @@ -110,9 +110,10 @@ static void show_faulting_vma(unsigned long address, char *buf)
> vma->vm_start < TASK_UNMAPPED_BASE ?
> address : address - vma->vm_start,
> nm, vma->vm_start, vma->vm_end);
> - } else {
> + } else
> pr_info(" @No matching VMA found\n");
> - }
> +
> + up_read(¤t->active_mm->mmap_sem);
> }
>
> static void show_ecr_verbose(struct pt_regs *regs)
>
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