RTEMS 5.1 pc686 BSP malloc_info problem?

[Gedare Bloom]

On Thu, Oct 15, 2020 at 6:35 AM Joel Sherrill <joel at rtems.org> wrote:
>
>
>
> On Thu, Oct 15, 2020, 7:15 AM Alan Cudmore <alan.cudmore at gmail.com> wrote:
>>
>> Thanks for all of the help, and thanks for the patch Chris! I was
>> hoping to submit a patch this weekend, so you just gave me back some
>> time :)
>
>
> Glad you found this!
>
> The RFS was new in 4.10 as I recall. You guys have missions using this. Do you need to locally fix this?
>
> It also needs to be fixed in 4.11.
>
> For posterity, if a fix is needed for 4.10, should we push it even though we have no plans for a future release from that branch? Just asking since a small number of other patches have been pushed to that branch.
>
Yes.

>
>
>> Alan
>>
>> On Thu, Oct 15, 2020 at 2:08 AM Chris Johns <chrisj at rtems.org> wrote:
>> >
>> > On 13/10/20 4:13 am, Joel Sherrill wrote:
>> > > On Mon, Oct 12, 2020 at 11:15 AM Alan Cudmore <alan.cudmore at gmail.com
>> > > <mailto:alan.cudmore at gmail.com>> wrote:
>> > >
>> > >     Hi Chris,
>> > >     I'm not sure that I can easily create a test to show that this
>> > >     condition exists. I think the rtems_rfs_bitmap_create_search function
>> > >     works as it is intended to, but during the last iteration of the for
>> > >     loop, if 'size' is zero and 'bit' is 31, the 'search_map' variable is
>> > >     incremented once more, and the value of RTEMS_RFS_BITMAP_ELEMENT_CLEAR
>> > >     (0xFFFFFFFF) is written to that location. This location is one address
>> > >     beyond the memory that was allocated for the search_map in
>> > >     rtems_rfs_bitmap_open.
>> > >     I guess that most of the time this is a silent side effect, but my
>> > >     application just happened to have memory lined up such that the extra
>> > >     write causes the malloc Allocator mutex to fail, causing the
>> > >     malloc_info call to block indefinitely. I would consider this a lucky
>> > >     break!
>> > >     The exact same example application does not fail on RTEMS 4.11. I
>> > >     think the problem still exists, but in that case, the word that gets
>> > >     written is different.
>> > >
>> > >     Here are some debug printfs from rtems_rfs_bitmap_open and
>> > >     rtems_rfs_bitmap_create_search:
>> > >
>> > >     From rtems_rfs_bitmap_open:
>> > >     RFS - rtems_rfs_bitmap_open - search_bits malloced size = 16 bytes
>> > >     RFS - rtems_rfs_bitmap_open - addr of search_bits = 0x00C03814
>> > >     RFS -> size of search_map = 4
>> > >     RFS -> control->size = 4095
>> > >
>> > >     From the subsequent call to rtems_rfs_bitmap_create_search:
>> > >     These printfs are in the if clause where bit == 31 (line 633)
>> > >     RFS --> search_map before increment addr 00C03814, size = 3071
>> > >     RFS --> search_map after increment -> writing
>> > >     RTEMS_RFS_BITMAP_ELEMENT_CLEAR (-1) to addr 00C03818
>> > >     RFS --> search_map before increment addr 00C03818, size = 2047
>> > >     RFS --> search_map after increment -> writing
>> > >     RTEMS_RFS_BITMAP_ELEMENT_CLEAR (-1) to addr 00C0381C
>> > >     RFS --> search_map before increment addr 00C0381C, size = 1023
>> > >     RFS --> search_map after increment -> writing
>> > >     RTEMS_RFS_BITMAP_ELEMENT_CLEAR (-1) to addr 00C03820
>> > >     RFS --> search_map before increment addr 00C03820, size = 0
>> > >     RFS --> search_map after increment -> writing
>> > >     RTEMS_RFS_BITMAP_ELEMENT_CLEAR (-1) to addr 00C03824
>> > >
>> > >     It's this last write to 00C03824 that causes the problem. I think the
>> > >     fix just involves checking to see if size == 0 before executing the if
>> > >     clause. I wanted to be sure that this extra write was not needed.
>> > >
>> > >     If you have an idea for a test case, I can work on it, but if you
>> > >     think that this is good enough, I can propose a patch.
>> > >
>> > >     Also, thanks for the idea of using RTEMS_DEBUG Sebastian, I need to
>> > >     upgrade my RTEMS toolbox with the latest techniques.
>> > >
>> > >
>> > > If, while analysing this issues, you came up with any consistency checks
>> > > or assertions that can be added to the code when debug is enabled,
>> > > those would be welcomed. It is hard to go back and add them without
>> > > the analysis like you did hunting this bug.
>> >
>> > I have added an _Assert (thanks Sebastian) and I now see:
>> >
>> > *** BEGIN OF TEST FSRFSBITMAP 1 ***
>> >
>> > *** TEST VERSION: 6.0.0.df9cc1aee87da6c6ba41d52454fa5f45fba74501
>> >
>> > *** TEST STATE: EXPECTED_PASS
>> >
>> > *** TEST BUILD: RTEMS_DEBUG
>> >
>> > *** TEST TOOLS: 10.2.1 20200918 (RTEMS 6, RSB
>> > ed5030bc24dbfdfac52074ed78cf4231bf1f353d, Newlib 749cbcc)
>> > Initializing filesystem RFS
>> >
>> > assertion "search_map >= control->search_bits && search_map <
>> > (control->search_bits +
>> > rtems_rfs_bitmap_elements(rtems_rfs_bitmap_elements(control->size)))" failed:
>> > file "../../../cpukit/libfs/src/rfs/rtems-rfs-bitmaps.c", line 648, function:
>> > rtems_rfs_bitmap_create_search
>> >
>> >
>> >
>> > I have a patch to fix this I will post.
>> >
>> > Thank you Alan for the report and the analysis. It made my job nice and simple.
>> >
>> > Chris
>
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