[patch] fix hung fio process with large I/O sizes and verify= option

[patch] fix hung fio process with large I/O sizes and verify= option

[Jeff Moyer]

Hi,

If you use a very large I/O size (1G in this instance), and also specify
the verify option, fio will hang, using up 100% cpu, for ever and ever.
The problem is that __fill_random_buf_percentage does math that
overflows the size of an unsigned int.  Fixing that gets fio to
terminate as expected.

Here is the job file which showed the problem:

[global]
ioengine=dev-dax
direct=0
filename=/dev/dax0.0
verify=crc32c
bs=1G
[write]
rw=write
runtime=5
[read]
stonewall
rw=read
runtime=5

Reported-by: sujith_pandel@dell.com
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>

diff --git a/lib/rand.c b/lib/rand.c
index 46ffe4fb..99846a8d 100644
--- a/lib/rand.c
+++ b/lib/rand.c
@@ -156,7 +156,7 @@ void __fill_random_buf_percentage(unsigned long seed, void *buf,
 		/*
 		 * Fill random chunk
 		 */
-		this_len = (segment * (100 - percentage)) / 100;
+		this_len = ((unsigned long long)segment * (100 - percentage)) / 100;
 		if (this_len > len)
 			this_len = len;
 

Re: [patch] fix hung fio process with large I/O sizes and verify= option

[Sitsofe Wheeler]

I'm not sure if you've overlooked this one Jens so I'm re-mentioning it...

On Fri, 28 Sep 2018 at 22:31, Jeff Moyer <jmoyer@redhat.com> wrote:
>
> Hi,
>
> If you use a very large I/O size (1G in this instance), and also specify
> the verify option, fio will hang, using up 100% cpu, for ever and ever.
> The problem is that __fill_random_buf_percentage does math that
> overflows the size of an unsigned int.  Fixing that gets fio to
> terminate as expected.
>
> Here is the job file which showed the problem:
>
> [global]
> ioengine=dev-dax
> direct=0
> filename=/dev/dax0.0
> verify=crc32c
> bs=1G
> [write]
> rw=write
> runtime=5
> [read]
> stonewall
> rw=read
> runtime=5
>
> Reported-by: sujith_pandel@dell.com
> Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
>
> diff --git a/lib/rand.c b/lib/rand.c
> index 46ffe4fb..99846a8d 100644
> --- a/lib/rand.c
> +++ b/lib/rand.c
> @@ -156,7 +156,7 @@ void __fill_random_buf_percentage(unsigned long seed, void *buf,
>                 /*
>                  * Fill random chunk
>                  */
> -               this_len = (segment * (100 - percentage)) / 100;
> +               this_len = ((unsigned long long)segment * (100 - percentage)) / 100;
>                 if (this_len > len)
>                         this_len = len;
>

-- 
Sitsofe | http://sucs.org/~sits/

Re: [patch] fix hung fio process with large I/O sizes and verify= option

[Jens Axboe]

On 9/28/18 3:27 PM, Jeff Moyer wrote:
> Hi,
> 
> If you use a very large I/O size (1G in this instance), and also specify
> the verify option, fio will hang, using up 100% cpu, for ever and ever.
> The problem is that __fill_random_buf_percentage does math that
> overflows the size of an unsigned int.  Fixing that gets fio to
> terminate as expected.
> 
> Here is the job file which showed the problem:
> 
> [global]
> ioengine=dev-dax
> direct=0
> filename=/dev/dax0.0
> verify=crc32c
> bs=1G
> [write]
> rw=write
> runtime=5
> [read]
> stonewall
> rw=read
> runtime=5
> 
> Reported-by: sujith_pandel@dell.com
> Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
> 
> diff --git a/lib/rand.c b/lib/rand.c
> index 46ffe4fb..99846a8d 100644
> --- a/lib/rand.c
> +++ b/lib/rand.c
> @@ -156,7 +156,7 @@ void __fill_random_buf_percentage(unsigned long seed, void *buf,
>  		/*
>  		 * Fill random chunk
>  		 */
> -		this_len = (segment * (100 - percentage)) / 100;
> +		this_len = ((unsigned long long)segment * (100 - percentage)) / 100;
>  		if (this_len > len)
>  			this_len = len;

Thanks Jeff, applied.

-- 
Jens Axboe

Re: [patch] fix hung fio process with large I/O sizes and verify= option

[Jens Axboe]

On 9/30/18 3:35 AM, Sitsofe Wheeler wrote:
> I'm not sure if you've overlooked this one Jens so I'm re-mentioning it...

Thanks, now applied :)

-- 
Jens Axboe