On 13/10/20 4:13 am, Joel Sherrill wrote: > On Mon, Oct 12, 2020 at 11:15 AM Alan Cudmore <alan.cudm...@gmail.com > <mailto:alan.cudm...@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 _______________________________________________ devel mailing list devel@rtems.org http://lists.rtems.org/mailman/listinfo/devel