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 :) [...] > 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. [...]
