Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1204442

Re: [RFC PATCH] percpu: Prevent endless loop if there is no unallocated region (unicore32 bug)

Show all headers | View raw

On 08/10/2015 09:36 AM, Tejun Heo wrote:
> Hello,
>
> On Sun, Aug 09, 2015 at 05:17:39AM -0700, Guenter Roeck wrote:
>> Qemu tests with unicore32 show memory management code entering an endless
>> loop in pcpu_alloc(). Bisect points to commit a93ace487a33 ("percpu: move
>> region iterations out of pcpu_[de]populate_chunk()"). Code analysis
>> identifies the following relevant changes.
>>
>> -       rs = page_start;
>> -       pcpu_next_pop(chunk, &rs, &re, page_end);
>> -
>> -       if (rs != page_start || re != page_end) {
>> +       pcpu_for_each_unpop_region(chunk, rs, re, page_start, page_end) {
>>
>> For unicore32, values were page_start==0, page_end==1, rs==0, re==1.
>> This worked fine with the old code. With the new code, however, the loop
>> is always entered. Debugging information added into the loop shows
>> an endless repetition of
>>
>> in loop chunk c5c53100 populated 0xff rs 1 re 2 page start 0 page end 1
>> in loop chunk c5c53100 populated 0xff rs 1 re 2 page start 0 page end 1
>> in loop chunk c5c53100 populated 0xff rs 1 re 2 page start 0 page end 1
>> in loop chunk c5c53100 populated 0xff rs 1 re 2 page start 0 page end 1
>
> That's a bug in the find bit functions in unicore32.  If @offset >=
> @end, it should return @end, not @offset.
>

Yes, your are right, the find next functions in unicore32 are wrong.

Sorry for the noise - I should have checked more closely. Copying the maintainer.

Thanks,
Guenter

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

[RFC PATCH] percpu: Prevent endless loop if there is no unallocated region Guenter Roeck <linux@roeck-us.net> - 2015-08-09 14:20 +0200
  Re: [RFC PATCH] percpu: Prevent endless loop if there is no  unallocated region Tejun Heo <tj@kernel.org> - 2015-08-10 18:40 +0200
    Re: [RFC PATCH] percpu: Prevent endless loop if there is no unallocated  region (unicore32 bug) Guenter Roeck <linux@roeck-us.net> - 2015-08-10 19:20 +0200

csiph-web