Re: [PATCH] powerpc/mm: Fix missing mmap_sem release
From: Laurent Dufour
Date: Fri Sep 08 2017 - 03:08:21 EST
On 07/09/2017 22:51, Davidlohr Bueso wrote:
> On Thu, 07 Sep 2017, Laurent Dufour wrote:
>> The commit b5c8f0fd595d ("powerpc/mm: Rework mm_fault_error()") reviewed
>> the way the error path is managed in __do_page_fault() but it was a bit too
>> agressive when handling a case by returning without releasing the mmap_sem.
>> By the way, replacing current->mm->mmap_sem by mm->mmap_sem as mm is set to
>> Fixes: b5c8f0fd595d ("powerpc/mm: Rework mm_fault_error()")
>> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
>> Signed-off-by: Laurent Dufour <laurent.du4@xxxxxxx>
>> arch/powerpc/mm/fault.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
>> index 4797d08581ce..f799ccf37d27 100644
>> --- a/arch/powerpc/mm/fault.c
>> +++ b/arch/powerpc/mm/fault.c
> But... here:
> * If we need to retry the mmap_sem has already been released,
> * and if there is a fatal signal pending there is no guarantee
> * that we made any progress. Handle this case first.
>> @@ -521,10 +521,11 @@ static int __do_page_fault(struct pt_regs *regs,
>> unsigned long address,
>> * User mode? Just return to handle the fatal exception otherwise
>> * return to bad_page_fault
>> + up_read(&mm->mmap_sem);
>> return is_user ? 0 : SIGBUS;
> Per the above comment, for that case handle_mm_fault()
> has already released mmap_sem. The same occurs in x86,
> for example.
Oops, my bad.
Please forget about this stupid patch...