Re: [PATCH 08/10] parisc: fix livelock in uaccess

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Hi Al,

On 1/31/23 21:06, Al Viro wrote:
parisc equivalent of 26178ec11ef3 "x86: mm: consolidate VM_FAULT_RETRY handling"
If e.g. get_user() triggers a page fault and a fatal signal is caught, we might
end up with handle_mm_fault() returning VM_FAULT_RETRY and not doing anything
to page tables.  In such case we must *not* return to the faulting insn -
that would repeat the entire thing without making any progress; what we need
instead is to treat that as failed (user) memory access.

Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
  arch/parisc/mm/fault.c | 5 ++++-
  1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/parisc/mm/fault.c b/arch/parisc/mm/fault.c
index 869204e97ec9..bb30ff6a3e19 100644
--- a/arch/parisc/mm/fault.c
+++ b/arch/parisc/mm/fault.c
@@ -308,8 +308,11 @@ void do_page_fault(struct pt_regs *regs, unsigned long code,

  	fault = handle_mm_fault(vma, address, flags, regs);

-	if (fault_signal_pending(fault, regs))
+	if (fault_signal_pending(fault, regs)) {
+		if (!user_mode(regs))
+			goto no_context;
+	}

The testcase in
does hang with and without above patch on parisc.
It does not consume CPU in that state and can be killed with ^C.

Any idea?


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