On 06/08/2021 04.46, Yunsheng Lin wrote:
+static inline long page_pool_atomic_sub_frag_count_return(struct page *page,
+ long nr)
+{
+ long ret;
+
+ /* As suggested by Alexander, atomic_long_read() may cover up the
+ * reference count errors, so avoid calling atomic_long_read() in
+ * the cases of freeing or draining the page_frags, where we would
+ * not expect it to match or that are slowpath anyway.
+ */
+ if (__builtin_constant_p(nr) &&
+ atomic_long_read(&page->pp_frag_count) == nr)
+ return 0;
+
+ ret = atomic_long_sub_return(nr, &page->pp_frag_count);
+ WARN_ON(ret < 0);
I worried about this WARN_ON() as it generates an 'ud2' instruction
which influence I-cache fetching. But I have disassembled (objdump) the
page_pool.o binary and the ud2 gets placed last in the main function
page_pool_put_page() that use this inlined function.
Thus, I assume this is not a problem :-)
+ return ret;
