riscv: Fixup race condition on PG_dcache_clean in flush_icache_pte

In commit 588a513 ("arm64: Fix race condition on PG_dcache_clean
in __sync_icache_dcache()"), we found RISC-V has the same issue as the
previous arm64. The previous implementation didn't guarantee the correct
sequence of operations, which means flush_icache_all() hasn't been
called when the PG_dcache_clean was set. That would cause a risk of page
synchronization.

Fixes: 08f051e ("RISC-V: Flush I$ when making a dirty page executable")
Signed-off-by: Guo Ren <[email protected]>
Signed-off-by: Guo Ren <[email protected]>
Reviewed-by: Andrew Jones <[email protected]>
Reviewed-by: Conor Dooley <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Cc: [email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: guoren83

arch/riscv/mm/cacheflush.c

@@ -90,8 +90,10 @@ void flush_icache_pte(pte_t pte)
 	if (PageHuge(page))
 		page = compound_head(page);
 
-	if (!test_and_set_bit(PG_dcache_clean, &page->flags))
+	if (!test_bit(PG_dcache_clean, &page->flags)) {
 		flush_icache_all();
+		set_bit(PG_dcache_clean, &page->flags);
+	}
 }
 #endif /* CONFIG_MMU */