RTEMS 5.1 pc686 BSP malloc_info problem?

[Joel Sherrill]

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.



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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