On Wednesday 02 March 2016 14:21:29 Dan Carpenter wrote: > On Wed, Mar 02, 2016 at 11:52:29AM +0100, Arnd Bergmann wrote: > > Did you find more of these? > > > > it doesn't matter much either way, but if you do multiple such patches, > > One or two. I already sent the fixes. I think it was applied. > > > I'd suggest using a single PTR_ERR_OR_ZERO() instead of IS_ERR()+PTR_ERR(). > > > > I have found a couple of drivers in which that leads to better object > > code, and avoids a warning about a possibly uninitialized variable > > when the function gets inlined into another one (which won't happen > > for this driver). > > Huh? I sent one where I could have done that but I deliberately didn't > because I wanted the uninitialized warning if I made a mistake. It > sounds like you're working around a GCC bug... The uninitialized warning here is about a type mismatch preventing gcc from noticing that two conditions are the same, I'm not sure if this is a bug in gcc, or required by the C standard. I don't think there is a way in which you would hide a correct warning about an uninitialized warning. Have a look at https://git.kernel.org/cgit/linux/kernel/git/gfs2/linux-gfs2.git/commit/fs/gfs2?h=for-next&id=07cfdc3071432a07713e4d007c2811e0224490b0 in which get_leaf_nr() uses the IS_ERR()/PTR_ERR() combo to return an error from a pointer, or return success when the pointer was set, followed by a warning about the use of the pointer in another function. My original patch avoided the warning by using IS_ERR_VALUE() in the caller, but in retrospect, IS_ERR_OR_ZERO() would have been a nicer solution: @@ -783,12 +783,15 @@ static int get_leaf_nr(struct gfs2_inode *dip, u32 index, u64 *leaf_out) { __be64 *hash; + int error; hash = gfs2_dir_get_hash_table(dip); - if (IS_ERR(hash)) - return PTR_ERR(hash); - *leaf_out = be64_to_cpu(*(hash + index)); - return 0; + error = PTR_ERR_OR_ZERO(hash); + + if (!error) + *leaf_out = be64_to_cpu(*(hash + index)); + + return error; } and I've used that elsewhere now when I ran into this kind of false positive warning. Arnd -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
