[PATCH 00/38] Fixes related to incorrect usage of unsigned types

[PATCH 00/38] Fixes related to incorrect usage of unsigned types

[Andrzej Hajda]

Hi,

This is set of independent patches. The only connection between
them is that they try to address problems spotted by proposed
coccinelle semantic patch unsigned_lesser_than_zero.cocci[1].

Semantic patch finds comparisons of types:
    unsigned < 0
    unsigned >= 0
The former is always false, the latter is always true.
Such comparisons are useless, so theoretically they could be
safely removed, but their presence quite often indicates bugs.

This patchset contains mainly real bug fixes(patches 01-25),
usually type fixes.

Patches 26-37 removes unnecessary checks. Semantic patch found
much more such places (more than 80), but since every case needs
some analysis I have decided to leave them for antoher patchset.

The last patch should be probably replaced with something better,
I guess it should be treated rather as bug report.

The patches are based on linux-next (20150918).

Patches were only compile tested, so please look at them carefully.

I have sent all patches to linux-kernel mailing list. Individual
patches + cover letter went also to apropriate addresses,
according to get_maintainers.pl script.

One more thing. To fullfill different maintaner/subsystem requirements
I have decided to prefix patch subjects with prefixes present in
last 10 commits for affected files. I am not sure if this is the
best solution, if there are any better solutions please let me know :)

[1]: http://permalink.gmane.org/gmane.linux.kernel/2038576

Regards
Andrzej


Andrzej Hajda (38):
  arm-cci: fix handling cpumask_any_but return value
  bus: arm-ccn: fix handling cpumask_any_but return value
  drm/i915: fix handling gen8_emit_flush_coherentl3_wa result
  IB/ehca: fix handling idr_alloc result
  staging: lustre: fix handling lustre_posix_acl_xattr_filter result
  tty: serial: lpc32xx_hs: fix handling platform_get_irq result
  usb: host: ehci-msm: fix handling platform_get_irq result
  openvswitch: fix handling result of ipv6_skip_exthdr
  selftests/timers: fix write return value handlng
  hwrng: fix handling platform_get_irq
  HSI: omap_ssi: fix handling ida_simple_get result
  HSI: omap_ssi_port: fix handling of_get_named_gpio result
  ARM: shmobile: apmu: correct type of CPU id
  clk: vt8500: fix sign of possible PLL values
  drm/layerscape: fix handling fsl_dcu_drm_plane_index result
  gpu: ipu-v3: fix div_ratio type
  isdn: hisax: fix frame calculation
  net/ibm/emac: fix type of phy_mode
  net: stmmac: fix type of entry variable
  net: brcm80211: fix range check
  mwifiex: fix comparison expression
  orinoco: fix checking for default value
  rndis_wlan: fix checking for default value
  rtc: opal: fix type of token
  staging: media: davinci_vpfe: fix ipipe_mode type
  staging: lustre: remove invalid check
  usbnet: remove invalid check
  video/omap: remove invalid check
  Input: touchscreen: atmel: remove invalid check
  leds: flash: remove invalid check
  leds: tca6507: remove invalid check
  fs/cachefiles: remove invalid checks
  mm/memblock.c: remove invalid check
  perf: remove invalid check
  ptrace: remove invalid check
  MIPS: remove invalid check
  zlib_deflate/deftree: change always true condition to 1
  drm/radeon: simplify boot level calculation

 arch/arm/mach-shmobile/platsmp-apmu.c               |  2 +-
 arch/mips/mm/sc-mips.c                              |  4 ++--
 arch/sh/kernel/ptrace_32.c                          |  3 +--
 arch/sh/kernel/ptrace_64.c                          |  4 ++--
 drivers/bus/arm-cci.c                               |  2 +-
 drivers/bus/arm-ccn.c                               |  2 +-
 drivers/char/hw_random/xgene-rng.c                  |  7 ++++---
 drivers/clk/clk-vt8500.c                            |  6 +++---
 drivers/gpu/drm/amd/amdgpu/kv_dpm.c                 | 11 +----------
 drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_plane.c         |  3 ++-
 drivers/gpu/drm/i915/intel_lrc.c                    |  7 ++++---
 drivers/gpu/drm/radeon/kv_dpm.c                     | 11 +----------
 drivers/gpu/ipu-v3/ipu-csi.c                        |  2 +-
 drivers/hsi/controllers/omap_ssi.c                  |  7 +++----
 drivers/hsi/controllers/omap_ssi_port.c             |  8 ++++----
 drivers/input/touchscreen/atmel_mxt_ts.c            |  2 +-
 drivers/isdn/hisax/hfc4s8s_l1.c                     | 10 +++++-----
 drivers/leds/led-class-flash.c                      |  2 +-
 drivers/leds/leds-tca6507.c                         |  2 +-
 drivers/net/ethernet/ibm/emac/core.h                |  2 +-
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c   |  2 +-
 drivers/net/usb/lan78xx.c                           |  5 -----
 drivers/net/usb/smsc75xx.c                          |  5 -----
 drivers/net/usb/smsc95xx.c                          |  5 -----
 drivers/net/wireless/brcm80211/brcmsmac/main.c      |  2 +-
 drivers/net/wireless/mwifiex/11n_rxreorder.c        |  4 ++--
 drivers/net/wireless/orinoco/cfg.c                  |  6 +++---
 drivers/net/wireless/rndis_wlan.c                   |  2 +-
 drivers/rtc/rtc-opal.c                              |  4 ++--
 drivers/staging/lustre/lustre/llite/xattr.c         |  7 ++++---
 drivers/staging/lustre/lustre/osc/lproc_osc.c       |  3 ---
 drivers/staging/media/davinci_vpfe/dm365_ipipe_hw.c |  2 +-
 drivers/staging/rdma/ehca/ehca_cq.c                 | 13 +++++++------
 drivers/tty/serial/lpc32xx_hs.c                     |  7 ++++---
 drivers/usb/host/ehci-msm.c                         |  6 +++---
 drivers/video/fbdev/omap/omapfb_main.c              |  5 -----
 fs/cachefiles/bind.c                                |  9 +++------
 fs/cachefiles/daemon.c                              |  6 +++---
 lib/zlib_deflate/deftree.c                          |  2 +-
 mm/memblock.c                                       |  2 +-
 net/openvswitch/conntrack.c                         |  2 +-
 tools/testing/selftests/timers/clocksource-switch.c |  2 +-
 42 files changed, 79 insertions(+), 119 deletions(-)

-- 
1.9.1

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[PATCH 33/38] mm/memblock.c: remove invalid check

[Andrzej Hajda]

Unsigned value cannot be lesser than zero.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2038576

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
---
 mm/memblock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index d300f13..aeb5148 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -837,7 +837,7 @@ void __init_memblock __next_reserved_mem_region(u64 *idx,
 {
 	struct memblock_type *type = &memblock.reserved;
 
-	if (*idx >= 0 && *idx < type->cnt) {
+	if (*idx < type->cnt) {
 		struct memblock_region *r = &type->regions[*idx];
 		phys_addr_t base = r->base;
 		phys_addr_t size = r->size;
-- 
1.9.1

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Re: [PATCH 00/38] Fixes related to incorrect usage of unsigned types

[David Howells]

Andrzej Hajda <a.hajda@samsung.com> wrote:

> Semantic patch finds comparisons of types:
>     unsigned < 0
>     unsigned >= 0
> The former is always false, the latter is always true.
> Such comparisons are useless, so theoretically they could be
> safely removed, but their presence quite often indicates bugs.

Or someone has left them in because they don't matter and there's the
possibility that the type being tested might be or become signed under some
circumstances.  If the comparison is useless, I'd expect the compiler to just
discard it - for such cases your patch is pointless.

If I have, for example:

	unsigned x;

	if (x == 0 || x > 27)
		give_a_range_error();

I will write this as:

	unsigned x;

	if (x <= 0 || x > 27)
		give_a_range_error();

because it that gives a way to handle x being changed to signed at some point
in the future for no cost.  In which case, your changing the <= to an ==
"because the < part of the case is useless" is arguably wrong.

David

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Re: [PATCH 33/38] mm/memblock.c: remove invalid check

[Andrew Morton]

On Mon, 21 Sep 2015 15:34:05 +0200 Andrzej Hajda <a.hajda@samsung.com> wrote:

> Unsigned value cannot be lesser than zero.
> 
> The problem has been detected using proposed semantic patch
> scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].
> 
> [1]: http://permalink.gmane.org/gmane.linux.kernel/2038576
> 
> ...
>
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -837,7 +837,7 @@ void __init_memblock __next_reserved_mem_region(u64 *idx,
>  {
>  	struct memblock_type *type = &memblock.reserved;
>  
> -	if (*idx >= 0 && *idx < type->cnt) {
> +	if (*idx < type->cnt) {

Linus has in the past expressed a preference for retaining checks such
as this.  iirc he finds it clearer.  And perhaps safer if the type
should change in the future.


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Re: [PATCH 00/38] Fixes related to incorrect usage of unsigned types

[Andrzej Hajda]

On 09/21/2015 03:42 PM, David Howells wrote:
> Andrzej Hajda <a.hajda-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org> wrote:
> 
>> Semantic patch finds comparisons of types:
>>     unsigned < 0
>>     unsigned >= 0
>> The former is always false, the latter is always true.
>> Such comparisons are useless, so theoretically they could be
>> safely removed, but their presence quite often indicates bugs.
> 
> Or someone has left them in because they don't matter and there's the
> possibility that the type being tested might be or become signed under some
> circumstances.  If the comparison is useless, I'd expect the compiler to just
> discard it - for such cases your patch is pointless.
> 
> If I have, for example:
> 
> 	unsigned x;
> 
> 	if (x == 0 || x > 27)
> 		give_a_range_error();
> 
> I will write this as:
> 
> 	unsigned x;
> 
> 	if (x <= 0 || x > 27)
> 		give_a_range_error();
> 
> because it that gives a way to handle x being changed to signed at some point
> in the future for no cost.  In which case, your changing the <= to an ==
> "because the < part of the case is useless" is arguably wrong.

This is why I have not checked for such cases - I have skipped checks of type
	unsigned <= 0
exactly for the reasons above.

However I have left two other checks as they seems to me more suspicious - they
are always true or false. But as Dmitry and Andrew pointed out Linus have quite
strong opinion against removing range checks in such cases as he finds it
clearer. I think it applies to patches 29-36. I am not sure about patches 26-28,37.

Regards
Andrzej

> 
> David
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Re: [PATCH 00/38] Fixes related to incorrect usage of unsigned types

[Jacek Anaszewski]

On 09/22/2015 11:13 AM, Andrzej Hajda wrote:
> On 09/21/2015 03:42 PM, David Howells wrote:
>> Andrzej Hajda <a.hajda-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org> wrote:
>>
>>> Semantic patch finds comparisons of types:
>>>      unsigned < 0
>>>      unsigned >= 0
>>> The former is always false, the latter is always true.
>>> Such comparisons are useless, so theoretically they could be
>>> safely removed, but their presence quite often indicates bugs.
>>
>> Or someone has left them in because they don't matter and there's the
>> possibility that the type being tested might be or become signed under some
>> circumstances.  If the comparison is useless, I'd expect the compiler to just
>> discard it - for such cases your patch is pointless.
>>
>> If I have, for example:
>>
>> 	unsigned x;
>>
>> 	if (x == 0 || x > 27)
>> 		give_a_range_error();
>>
>> I will write this as:
>>
>> 	unsigned x;
>>
>> 	if (x <= 0 || x > 27)
>> 		give_a_range_error();
>>
>> because it that gives a way to handle x being changed to signed at some point
>> in the future for no cost.  In which case, your changing the <= to an ==
>> "because the < part of the case is useless" is arguably wrong.
>
> This is why I have not checked for such cases - I have skipped checks of type
> 	unsigned <= 0
> exactly for the reasons above.
>
> However I have left two other checks as they seems to me more suspicious - they
> are always true or false. But as Dmitry and Andrew pointed out Linus have quite
> strong opinion against removing range checks in such cases as he finds it
> clearer. I think it applies to patches 29-36. I am not sure about patches 26-28,37.

Dropped 30/38 and 31/38 from LED tree then.

-- 
Best Regards,
Jacek Anaszewski

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