riscv: fix livelock in uaccess

riscv 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.

Tested-by: Björn Töpel <bjorn@kernel.org>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index d86f7ce..c91d853 100644 (file)
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -324,8 +324,11 @@ good_area:
         * signal first. We do not need to release the mmap_lock because it
         * would already be released in __lock_page_or_retry in mm/filemap.c.
         */
-       if (fault_signal_pending(fault, regs))
+       if (fault_signal_pending(fault, regs)) {
+               if (!user_mode(regs))
+                       no_context(regs, addr);
                return;
+       }
 
        /* The fault is fully completed (including releasing mmap lock) */
        if (fault & VM_FAULT_COMPLETED)