On 12/09/2013 06:18 PM, James Hogan wrote: > On 09/12/13 10:11, Chen Gang wrote: >>> Since the metag compiler is stuck on an old version (gcc 4.2.4), which >>> is wrong to warn in this case, and newer versions of gcc don't appear to >>> warn about it anyway (I just checked with gcc 4.7.2 x86_64), I have no >>> objection to this warning remaining in the metag build. >>> >> >> Do you try "EXTRA_CFLAGS=-W" with gcc 4.7.2? I guess it will report the >> warning too, I don't feel the compiler is smart enough (except it lets >> the long function zswap_get_swap_cache_page really inline) :-) > > EXTRA_CFLAGS=-W on gcc 4.7.2 gives me plenty of pointless unused > parameter warnings when compiling mm/zswap.o, but not the warning you're > trying to silence. > Yeah, it will generate plenty of pointless warnings, although we still can often find valuable bugs in these warnings. Oh, I tried gcc 4.6.3-2 rhel version, get the same result as yours (do not report warning), but for me, it is still a compiler's bug, it *should* report a warning for it, we can try below: - modify zswap_get_swap_cache_page() to let it may return another value (one sample modification is in attachment) - compile again, it doesn't report related warning, either - in this case, it *should* report related warning. Could you help to try it under gcc 4.7.2, thanks? BTW: gcc really exists some bugs about uninitialized variable, e.g. one known bug: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18501 kernel related: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57856 Thanks. -- Chen Gang Open, share, and attitude like air, water and life which God blessed
diff --git a/mm/zswap.c b/mm/zswap.c index 5a63f78..1853ef4 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -469,8 +469,7 @@ static int zswap_get_swap_cache_page(swp_entry_t entry, */ err = radix_tree_preload(GFP_KERNEL); if (err) - break; - + return -4; /* * Swap entry may have been freed since our caller observed it. */