linux-kernel - Re: [PATCH 1/2] IB/hfi1: Fix a parameter of find_first

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Message-ID: <2c923344-04c8-cdbd-ac06-047027f7a23a@redhat.com>
Date:   Fri, 26 Aug 2016 14:01:55 -0400
From:   Doug Ledford <dledford@...hat.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        mike.marciniszyn@...el.com, dennis.dalessandro@...el.com,
        sean.hefty@...el.com, hal.rosenstock@...il.com
Cc:     linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 1/2] IB/hfi1: Fix a parameter of find_first_bit.

On 8/26/2016 9:35 AM, Doug Ledford wrote:
> On 8/26/2016 12:49 AM, Christophe JAILLET wrote:
>> The 2nd parameter of 'find_first_bit' is the number of bits to search.
>> In this case, we are passing 'sizeof(unsigned long)' which is likely to
>> be 4 or 8.
> 
> If the size can be 4 or 8, then using 64 universally is not correct.
> Why not use sizeof() * 8 (or << 3)?

Better yet, why not put this patch in the kernel first:

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index d96a6118d26a..a8838c87668e 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -52,6 +52,8 @@

 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) +
__must_be_array(arr))

+#define bitsizeof(x)   (sizeof((x)) << 3)
+
 #define u64_to_user_ptr(x) (           \
 {                                      \
        typecheck(u64, x);              \

then start going around replacing all these hard coded numbers with the
use of bitsizeof().  It can be applied not just to the find_first*bit()
routines, but to a bunch of other routines too.  Just look at
include/linux/bitmap.h and any that have nbits as an argument are
candidates.


-- 
Doug Ledford <dledford@...hat.com>
    GPG Key ID: 0E572FDD



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