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[PATCH v3 0/4] lib/string_helpers: fix precision issues and introduce tests

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  [PATCH v3 0/4] lib/string_helpers: fix precision issues and introduce tests Vitaly Kuznetsov <vkuznets@redhat.com> - 2015-10-29 17:40 +0100
    [PATCH v3 4/4] lib/test-string_helpers.c: add string_get_size() tests Vitaly Kuznetsov <vkuznets@redhat.com> - 2015-10-29 17:40 +0100
      Re: [PATCH v3 4/4] lib/test-string_helpers.c: add string_get_size() tests Andy Shevchenko <andy.shevchenko@gmail.com> - 2015-10-29 22:40 +0100
    [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for string_get_size() interface Vitaly Kuznetsov <vkuznets@redhat.com> - 2015-10-29 17:40 +0100
      Re: [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for  string_get_size() interface James Bottomley <jbottomley@odin.com> - 2015-10-29 23:30 +0100
        Re: [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for string_get_size() interface Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-10-30 00:20 +0100
          Re: [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for string_get_size() interface Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-10-30 00:30 +0100
          Re: [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for  string_get_size() interface James Bottomley <jbottomley@odin.com> - 2015-10-30 04:40 +0100
        Re: [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for string_get_size() interface Vitaly Kuznetsov <vkuznets@redhat.com> - 2015-10-30 11:50 +0100
          Re: [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for  string_get_size() interface James Bottomley <jbottomley@odin.com> - 2015-10-31 01:30 +0100
    [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size() against blk_size=0 Vitaly Kuznetsov <vkuznets@redhat.com> - 2015-10-29 17:40 +0100
      Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size()  against blk_size=0 Andy Shevchenko <andy.shevchenko@gmail.com> - 2015-10-29 22:30 +0100
      Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size()  against blk_size=0 James Bottomley <jbottomley@odin.com> - 2015-10-30 00:10 +0100
        Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size()  against blk_size=0 Andy Shevchenko <andy.shevchenko@gmail.com> - 2015-10-30 00:40 +0100
          Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size()  against blk_size=0 James Bottomley <jbottomley@odin.com> - 2015-10-30 04:40 +0100
            Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size() against blk_size=0 Vitaly Kuznetsov <vkuznets@redhat.com> - 2015-10-30 11:50 +0100
              Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size()  against blk_size=0 James Bottomley <jbottomley@odin.com> - 2015-10-31 01:10 +0100

#1258906 — [PATCH v3 0/4] lib/string_helpers: fix precision issues and introduce tests

Linux always lies about your storage size when it has 4k sectors and its
size is big enough. E.g. a device with 8192 4k sectors will be reported as
"32.7 MB/32 MiB" while "33.5 MB/32 MiB" is expected. This series is
supposed to fix the issue by fixing calculation precision in
string_get_size() for all possible inputs.

PATCH 1/4 is a preparatory change, PATCH 2/4 adds additional protection
against blk_size=0 (nobody is supposed to call string_get_size() with
with blk_size=0, but better safe than sorry), PATCH 3/4 re-factors
string_get_size() fixing the issue, PATCH 4/4 introduces tests for
string_get_size().

PATCH 4/4 was previously sent as part of "lib/string_helpers.c: fix
infinite loop in string_get_size()" series but it is still not merged
upstream. In this submission I improve it and add additional tests to it.

Changes since v2:
- Separate blk_size check from Patch 3/4 to new Patch 2/4 [Andy Shevchenko]
- Slightly change the algorithm in Patch 3/4 [Rasmus Villemoes]

Vitaly Kuznetsov (4):
  lib/string_helpers: change blk_size to u32 for string_get_size()
    interface
  lib/string_helpers.c: protect string_get_size() against blk_size=0
  lib/string_helpers.c: don't lose precision in string_get_size()
  lib/test-string_helpers.c: add string_get_size() tests

 include/linux/string_helpers.h |  2 +-
 lib/string_helpers.c           | 38 ++++++++++++++-------------
 lib/test-string_helpers.c      | 58 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 79 insertions(+), 19 deletions(-)

-- 
2.4.3

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#1258907 — [PATCH v3 4/4] lib/test-string_helpers.c: add string_get_size() tests

Add a couple of simple tests for string_get_size().

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 lib/test-string_helpers.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/lib/test-string_helpers.c b/lib/test-string_helpers.c
index 8e376ef..4c77b54 100644
--- a/lib/test-string_helpers.c
+++ b/lib/test-string_helpers.c
@@ -326,6 +326,61 @@ out:
 	kfree(out_test);
 }
 
+#define string_get_size_maxbuf 16
+#define test_string_get_size_one(size, blk_size, exp_result10, exp_result2)    \
+	do {                                                                   \
+		BUILD_BUG_ON(sizeof(exp_result10) >= string_get_size_maxbuf);  \
+		BUILD_BUG_ON(sizeof(exp_result2) >= string_get_size_maxbuf);   \
+		__test_string_get_size((size), (blk_size), (exp_result10),     \
+				       (exp_result2));                         \
+	} while (0)
+
+
+static __init void __test_string_get_size(const u64 size, const u32 blk_size,
+					  const char *exp_result10,
+					  const char *exp_result2)
+{
+	char buf10[string_get_size_maxbuf];
+	char buf2[string_get_size_maxbuf];
+
+	string_get_size(size, blk_size, STRING_UNITS_10, buf10, sizeof(buf10));
+	string_get_size(size, blk_size, STRING_UNITS_2, buf2, sizeof(buf2));
+
+	if (!memcmp(buf10, exp_result10, strlen(exp_result10) + 1))
+		goto check_stringunits_2;
+
+	buf10[sizeof(buf10) - 1] = '\0';
+
+	pr_warn("Test 'test_string_get_size' failed!\n");
+	pr_warn("string_get_size(size = %llu, blk_size = %u, units = %s)\n",
+		size, blk_size, "STRING_UNITS_10");
+	pr_warn("expected: '%s', got '%s'\n", exp_result10, buf10);
+
+check_stringunits_2:
+	if (!memcmp(buf2, exp_result2, strlen(exp_result2) + 1))
+		return;
+
+	buf2[sizeof(buf2) - 1] = '\0';
+
+	pr_warn("Test 'test_string_get_size' failed!\n");
+	pr_warn("string_get_size(size = %llu, blk_size = %u, units = %s)\n",
+		size, blk_size, "STRING_UNITS_2");
+	pr_warn("expected: '%s', got '%s'\n", exp_result2, buf2);
+}
+
+static __init void test_string_get_size(void)
+{
+	test_string_get_size_one(16384, 512, "8.38 MB", "8.00 MiB");
+	test_string_get_size_one(500118192, 512, "256 GB", "238 GiB");
+	test_string_get_size_one(8192, 4096, "33.5 MB", "32.0 MiB");
+	test_string_get_size_one(1100, 1, "1.10 kB", "1.07 KiB");
+	test_string_get_size_one(3000, 1900, "5.70 MB", "5.43 MiB");
+	test_string_get_size_one(U64_MAX, 4096, "75.5 ZB", "63.9 ZiB");
+	test_string_get_size_one(1999, U32_MAX, "8.58 TB", "7.80 TiB");
+	test_string_get_size_one(1, 512, "512 B", "512 B");
+	test_string_get_size_one(0, 512, "0 B", "0 B");
+}
+
 static int __init test_string_helpers_init(void)
 {
 	unsigned int i;
@@ -344,6 +399,9 @@ static int __init test_string_helpers_init(void)
 	for (i = 0; i < (ESCAPE_ANY_NP | ESCAPE_HEX) + 1; i++)
 		test_string_escape("escape 1", escape1, i, TEST_STRING_2_DICT_1);
 
+	/* Test string_get_size() */
+	test_string_get_size();
+
 	return -EINVAL;
 }
 module_init(test_string_helpers_init);
-- 
2.4.3

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#1259027 — Re: [PATCH v3 4/4] lib/test-string_helpers.c: add string_get_size() tests

On Thu, Oct 29, 2015 at 6:30 PM, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
> Add a couple of simple tests for string_get_size().
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  lib/test-string_helpers.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 58 insertions(+)
>
> diff --git a/lib/test-string_helpers.c b/lib/test-string_helpers.c
> index 8e376ef..4c77b54 100644
> --- a/lib/test-string_helpers.c
> +++ b/lib/test-string_helpers.c
> @@ -326,6 +326,61 @@ out:
>         kfree(out_test);
>  }
>
> +#define string_get_size_maxbuf 16
> +#define test_string_get_size_one(size, blk_size, exp_result10, exp_result2)    \
> +       do {                                                                   \
> +               BUILD_BUG_ON(sizeof(exp_result10) >= string_get_size_maxbuf);  \
> +               BUILD_BUG_ON(sizeof(exp_result2) >= string_get_size_maxbuf);   \
> +               __test_string_get_size((size), (blk_size), (exp_result10),     \
> +                                      (exp_result2));                         \
> +       } while (0)
> +
> +
> +static __init void __test_string_get_size(const u64 size, const u32 blk_size,
> +                                         const char *exp_result10,
> +                                         const char *exp_result2)
> +{
> +       char buf10[string_get_size_maxbuf];
> +       char buf2[string_get_size_maxbuf];
> +
> +       string_get_size(size, blk_size, STRING_UNITS_10, buf10, sizeof(buf10));
> +       string_get_size(size, blk_size, STRING_UNITS_2, buf2, sizeof(buf2));
> +
> +       if (!memcmp(buf10, exp_result10, strlen(exp_result10) + 1))
> +               goto check_stringunits_2;
> +

> +       buf10[sizeof(buf10) - 1] = '\0';
> +
> +       pr_warn("Test 'test_string_get_size' failed!\n");
> +       pr_warn("string_get_size(size = %llu, blk_size = %u, units = %s)\n",
> +               size, blk_size, "STRING_UNITS_10");
> +       pr_warn("expected: '%s', got '%s'\n", exp_result10, buf10);

Looks to me as a helper function

test_string_get_size_pr_err(size, blk_size, units, exp_result, buf, buflen) {}

if (memcmp(buf10, exp_result10, strlen(exp_result10) + 1))
 _pr_err(...);

> +
> +check_stringunits_2:
> +       if (!memcmp(buf2, exp_result2, strlen(exp_result2) + 1))
> +               return;
> +
> +       buf2[sizeof(buf2) - 1] = '\0';
> +
> +       pr_warn("Test 'test_string_get_size' failed!\n");
> +       pr_warn("string_get_size(size = %llu, blk_size = %u, units = %s)\n",
> +               size, blk_size, "STRING_UNITS_2");
> +       pr_warn("expected: '%s', got '%s'\n", exp_result2, buf2);
> +}
> +
> +static __init void test_string_get_size(void)
> +{
> +       test_string_get_size_one(16384, 512, "8.38 MB", "8.00 MiB");
> +       test_string_get_size_one(500118192, 512, "256 GB", "238 GiB");
> +       test_string_get_size_one(8192, 4096, "33.5 MB", "32.0 MiB");
> +       test_string_get_size_one(1100, 1, "1.10 kB", "1.07 KiB");
> +       test_string_get_size_one(3000, 1900, "5.70 MB", "5.43 MiB");
> +       test_string_get_size_one(U64_MAX, 4096, "75.5 ZB", "63.9 ZiB");
> +       test_string_get_size_one(1999, U32_MAX, "8.58 TB", "7.80 TiB");
> +       test_string_get_size_one(1, 512, "512 B", "512 B");
> +       test_string_get_size_one(0, 512, "0 B", "0 B");

> +}
> +
>  static int __init test_string_helpers_init(void)
>  {
>         unsigned int i;
> @@ -344,6 +399,9 @@ static int __init test_string_helpers_init(void)
>         for (i = 0; i < (ESCAPE_ANY_NP | ESCAPE_HEX) + 1; i++)
>                 test_string_escape("escape 1", escape1, i, TEST_STRING_2_DICT_1);
>
> +       /* Test string_get_size() */
> +       test_string_get_size();
> +
>         return -EINVAL;
>  }
>  module_init(test_string_helpers_init);
> --
> 2.4.3
>
> --
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-- 
With Best Regards,
Andy Shevchenko
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#1258910 — [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for string_get_size() interface

string_get_size() can't really handle huge block sizes, especially
blk_size > U32_MAX but string_get_size() interface states the opposite.
Change blk_size from u64 to u32 to reflect the reality.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 include/linux/string_helpers.h | 2 +-
 lib/string_helpers.c           | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/string_helpers.h b/include/linux/string_helpers.h
index dabe643..1223e80 100644
--- a/include/linux/string_helpers.h
+++ b/include/linux/string_helpers.h
@@ -10,7 +10,7 @@ enum string_size_units {
 	STRING_UNITS_2,		/* use binary powers of 2^10 */
 };
 
-void string_get_size(u64 size, u64 blk_size, enum string_size_units units,
+void string_get_size(u64 size, u32 blk_size, enum string_size_units units,
 		     char *buf, int len);
 
 #define UNESCAPE_SPACE		0x01
diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index 5939f63..f6c27dc 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -26,7 +26,7 @@
  * at least 9 bytes and will always be zero terminated.
  *
  */
-void string_get_size(u64 size, u64 blk_size, const enum string_size_units units,
+void string_get_size(u64 size, u32 blk_size, const enum string_size_units units,
 		     char *buf, int len)
 {
 	static const char *const units_10[] = {
@@ -58,7 +58,7 @@ void string_get_size(u64 size, u64 blk_size, const enum string_size_units units,
 		i++;
 	}
 
-	exp = divisor[units] / (u32)blk_size;
+	exp = divisor[units] / blk_size;
 	/*
 	 * size must be strictly greater than exp here to ensure that remainder
 	 * is greater than divisor[units] coming out of the if below.
-- 
2.4.3

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#1259054 — Re: [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for string_get_size() interface

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#1259092 — Re: [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for string_get_size() interface

On Thu, Oct 29 2015, James Bottomley <jbottomley@odin.com> wrote:

> On Thu, 2015-10-29 at 17:30 +0100, Vitaly Kuznetsov wrote:
>> string_get_size() can't really handle huge block sizes, especially
>> blk_size > U32_MAX but string_get_size() interface states the opposite.
>> Change blk_size from u64 to u32 to reflect the reality.
>
> What is the actual evidence for this?  The calculation is designed to be
> a symmetric 128 bit multiply.  When I wrote and tested it, it worked
> fine for huge block sizes.
>

May I politely ask how you tested it, and what you mean by "worked"? The
bug I reported last week was particularly concerning block sizes >= 1024
(e.g. the 32768, 1024 pair giving 32.7 MB where the correct output would
be 33.5 MB). Now it turns out that it was actually broken for smaller
block sizes as well. For ~13000 semirandom size,blk_size pairs, the
current code produces the wrong result in ~2100 cases. The new code
reduces that to 122 cases, all of which are off by one in the last
digit.

And I don't buy the symmetry argument either. Mathematically, it should
give the same, but your algorithm produces 2.04 MB for 512,4096 and 2.09
MB for 4096,512.

Maybe the commit message could be better, but I think it makes a lot of
sense to make blk_size u32. Breaking the symmetry between size and
blk_size is good (less likely that the arguments get swapped). It
allows a simpler implementation. It makes the generated code
smaller.

Rasmus
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#1259099 — Re: [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for string_get_size() interface

On Fri, Oct 30 2015, Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote:

> block sizes as well. For ~13000 semirandom size,blk_size pairs,

Sorry, that should have been ~20000.

Rasmus
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#1259189 — Re: [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for string_get_size() interface

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#1259390 — Re: [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for string_get_size() interface

James Bottomley <jbottomley@odin.com> writes:

> On Thu, 2015-10-29 at 17:30 +0100, Vitaly Kuznetsov wrote:
>> string_get_size() can't really handle huge block sizes, especially
>> blk_size > U32_MAX but string_get_size() interface states the opposite.
>> Change blk_size from u64 to u32 to reflect the reality.
>
> What is the actual evidence for this?  The calculation is designed to be
> a symmetric 128 bit multiply.  When I wrote and tested it, it worked
> fine for huge block sizes.

We have 'u32 remainder' and then we do:

exp = divisor[units] / (u32)blk_size;
...
remainder = do_div(size, divisor[units]);
remainder *= blk_size;

I'm pretty sure it will overflow for some inputs.

>
> James
>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>>  include/linux/string_helpers.h | 2 +-
>>  lib/string_helpers.c           | 4 ++--
>>  2 files changed, 3 insertions(+), 3 deletions(-)
>> 
>> diff --git a/include/linux/string_helpers.h b/include/linux/string_helpers.h
>> index dabe643..1223e80 100644
>> --- a/include/linux/string_helpers.h
>> +++ b/include/linux/string_helpers.h
>> @@ -10,7 +10,7 @@ enum string_size_units {
>>  	STRING_UNITS_2,		/* use binary powers of 2^10 */
>>  };
>>  
>> -void string_get_size(u64 size, u64 blk_size, enum string_size_units units,
>> +void string_get_size(u64 size, u32 blk_size, enum string_size_units units,
>>  		     char *buf, int len);
>>  
>>  #define UNESCAPE_SPACE		0x01
>> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
>> index 5939f63..f6c27dc 100644
>> --- a/lib/string_helpers.c
>> +++ b/lib/string_helpers.c
>> @@ -26,7 +26,7 @@
>>   * at least 9 bytes and will always be zero terminated.
>>   *
>>   */
>> -void string_get_size(u64 size, u64 blk_size, const enum string_size_units units,
>> +void string_get_size(u64 size, u32 blk_size, const enum string_size_units units,
>>  		     char *buf, int len)
>>  {
>>  	static const char *const units_10[] = {
>> @@ -58,7 +58,7 @@ void string_get_size(u64 size, u64 blk_size, const enum string_size_units units,
>>  		i++;
>>  	}
>>  
>> -	exp = divisor[units] / (u32)blk_size;
>> +	exp = divisor[units] / blk_size;
>>  	/*
>>  	 * size must be strictly greater than exp here to ensure that remainder
>>  	 * is greater than divisor[units] coming out of the if below.

-- 
  Vitaly
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#1259875 — Re: [PATCH v3 1/4] lib/string_helpers: change blk_size to u32 for string_get_size() interface

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#1258911 — [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size() against blk_size=0

Division by zero happens if blk_size=0 is supplied to string_get_size().
Add WARN_ON() and set size to 0 to report '0 B'.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 lib/string_helpers.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index f6c27dc..ff3575b 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -50,6 +50,11 @@ void string_get_size(u64 size, u32 blk_size, const enum string_size_units units,
 
 	tmp[0] = '\0';
 	i = 0;
+
+	/* Calling string_get_size() with blk_size=0 is wrong! */
+	if (WARN_ON(!blk_size))
+		size = 0;
+
 	if (!size)
 		goto out;
 
-- 
2.4.3

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#1259014 — Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size() against blk_size=0

On Thu, Oct 29, 2015 at 6:30 PM, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
> Division by zero happens if blk_size=0 is supplied to string_get_size().
> Add WARN_ON() and set size to 0 to report '0 B'.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>

> ---
>  lib/string_helpers.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
> index f6c27dc..ff3575b 100644
> --- a/lib/string_helpers.c
> +++ b/lib/string_helpers.c
> @@ -50,6 +50,11 @@ void string_get_size(u64 size, u32 blk_size, const enum string_size_units units,
>
>         tmp[0] = '\0';
>         i = 0;
> +
> +       /* Calling string_get_size() with blk_size=0 is wrong! */
> +       if (WARN_ON(!blk_size))
> +               size = 0;
> +
>         if (!size)
>                 goto out;
>
> --
> 2.4.3
>
> --
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-- 
With Best Regards,
Andy Shevchenko
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#1259091 — Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size() against blk_size=0

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#1259104 — Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size() against blk_size=0

On Fri, Oct 30, 2015 at 1:00 AM, James Bottomley <jbottomley@odin.com> wrote:
> On Thu, 2015-10-29 at 17:30 +0100, Vitaly Kuznetsov wrote:
>> Division by zero happens if blk_size=0 is supplied to string_get_size().
>> Add WARN_ON() and set size to 0 to report '0 B'.
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>>  lib/string_helpers.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
>> index f6c27dc..ff3575b 100644
>> --- a/lib/string_helpers.c
>> +++ b/lib/string_helpers.c
>> @@ -50,6 +50,11 @@ void string_get_size(u64 size, u32 blk_size, const enum string_size_units units,
>>
>>       tmp[0] = '\0';
>>       i = 0;
>> +
>> +     /* Calling string_get_size() with blk_size=0 is wrong! */
>> +     if (WARN_ON(!blk_size))
>
> Get rid of the WARN_ON; it's the standard thing to do for a partially
> connected device.  Seeing zero is standard in a whole variety of
> situations.  SCSI shims the zero but most other drivers don't.

For *block* size? It will crash the kernel. I've checked, it wasn't
changed from the beginning (b9f28d863594).

+       exp = divisor[units] / (u32)blk_size;

-- 
With Best Regards,
Andy Shevchenko
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#1259188 — Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size() against blk_size=0

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#1259392 — Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size() against blk_size=0

James Bottomley <jbottomley@odin.com> writes:

> On Fri, 2015-10-30 at 01:32 +0200, Andy Shevchenko wrote:
>> On Fri, Oct 30, 2015 at 1:00 AM, James Bottomley <jbottomley@odin.com> wrote:
>> > On Thu, 2015-10-29 at 17:30 +0100, Vitaly Kuznetsov wrote:
>> >> Division by zero happens if blk_size=0 is supplied to string_get_size().
>> >> Add WARN_ON() and set size to 0 to report '0 B'.
>> >>
>> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> >> ---
>> >>  lib/string_helpers.c | 5 +++++
>> >>  1 file changed, 5 insertions(+)
>> >>
>> >> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
>> >> index f6c27dc..ff3575b 100644
>> >> --- a/lib/string_helpers.c
>> >> +++ b/lib/string_helpers.c
>> >> @@ -50,6 +50,11 @@ void string_get_size(u64 size, u32 blk_size, const enum string_size_units units,
>> >>
>> >>       tmp[0] = '\0';
>> >>       i = 0;
>> >> +
>> >> +     /* Calling string_get_size() with blk_size=0 is wrong! */
>> >> +     if (WARN_ON(!blk_size))
>> >
>> > Get rid of the WARN_ON; it's the standard thing to do for a partially
>> > connected device.  Seeing zero is standard in a whole variety of
>> > situations.  SCSI shims the zero but most other drivers don't.
>> 
>> For *block* size? It will crash the kernel. I've checked, it wasn't
>> changed from the beginning (b9f28d863594).
>
> The standard signal for a drive error in capacity is zero size and zero
> block size.  We have to take that case as standard without emitting
> scary warnings.

Ok, but what if size != 0? Is WARN_ON() justified in this case?

-- 
  Vitaly
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#1259870 — Re: [PATCH v3 2/4] lib/string_helpers.c: protect string_get_size() against blk_size=0

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