On Thu, Feb 21, 2019 at 10:29:56AM -0500, Jerome Glisse wrote: > On Tue, Feb 12, 2019 at 10:56:08AM +0800, Peter Xu wrote: > > The idea comes from the upstream discussion between Linus and Andrea: > > > > https://lkml.org/lkml/2017/10/30/560 > > > > A summary to the issue: there was a special path in handle_userfault() > > in the past that we'll return a VM_FAULT_NOPAGE when we detected > > non-fatal signals when waiting for userfault handling. We did that by > > reacquiring the mmap_sem before returning. However that brings a risk > > in that the vmas might have changed when we retake the mmap_sem and > > even we could be holding an invalid vma structure. > > > > This patch removes the special path and we'll return a VM_FAULT_RETRY > > with the common path even if we have got such signals. Then for all > > the architectures that is passing in VM_FAULT_ALLOW_RETRY into > > handle_mm_fault(), we check not only for SIGKILL but for all the rest > > of userspace pending signals right after we returned from > > handle_mm_fault(). This can allow the userspace to handle nonfatal > > signals faster than before. > > > > This patch is a preparation work for the next patch to finally remove > > the special code path mentioned above in handle_userfault(). > > > > Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > > Suggested-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> > > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> > > See maybe minor improvement > > Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx> > > [...] > > > diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c > > index 58f69fa07df9..c41c021bbe40 100644 > > --- a/arch/arm/mm/fault.c > > +++ b/arch/arm/mm/fault.c > > @@ -314,12 +314,12 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs) > > > > fault = __do_page_fault(mm, addr, fsr, flags, tsk); > > > > - /* If we need to retry but a fatal signal is pending, handle the > > + /* If we need to retry but a signal is pending, handle the > > * signal first. We do not need to release the mmap_sem because > > * it would already be released in __lock_page_or_retry in > > * mm/filemap.c. */ > > - if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) { > > - if (!user_mode(regs)) > > + if (unlikely(fault & VM_FAULT_RETRY && signal_pending(current))) { > > I rather see (fault & VM_FAULT_RETRY) ie with the parenthesis as it > avoids the need to remember operator precedence rules :) Yes it's good practise. I've been hit by the lock_page() days ago already so I think I'll remember (though this patch was earlier :) I'll fix all the places in the patch. Actually I noticed that there are four of them. And I've taken the r-b after the changes. Thanks, > > [...] > > > diff --git a/arch/nds32/mm/fault.c b/arch/nds32/mm/fault.c > > index 68d5f2a27f38..9f6e477b9e30 100644 > > --- a/arch/nds32/mm/fault.c > > +++ b/arch/nds32/mm/fault.c > > @@ -206,12 +206,12 @@ void do_page_fault(unsigned long entry, unsigned long addr, > > fault = handle_mm_fault(vma, addr, flags); > > > > /* > > - * If we need to retry but a fatal signal is pending, handle the > > + * If we need to retry but a signal is pending, handle the > > * signal first. We do not need to release the mmap_sem because it > > * would already be released in __lock_page_or_retry in mm/filemap.c. > > */ > > - if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) { > > - if (!user_mode(regs)) > > + if (fault & VM_FAULT_RETRY && signal_pending(current)) { > > Same as above parenthesis maybe. > > [...] > > > diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c > > index 0e8b6158f224..09baf37b65b9 100644 > > --- a/arch/um/kernel/trap.c > > +++ b/arch/um/kernel/trap.c > > @@ -76,8 +76,11 @@ int handle_page_fault(unsigned long address, unsigned long ip, > > > > fault = handle_mm_fault(vma, address, flags); > > > > - if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) > > + if (fault & VM_FAULT_RETRY && signal_pending(current)) { > > Same as above parenthesis maybe. > > [...] Regards, -- Peter Xu
