# git rev-parse -q --verify 2bc2026269beb0d7923317f5a4a28ce4d5bbc94c^{commit}
2bc2026269beb0d7923317f5a4a28ce4d5bbc94c
already have revision, skipping fetch
# git checkout -q -f -B kisskb 2bc2026269beb0d7923317f5a4a28ce4d5bbc94c
# git clean -qxdf
# < git log -1
# commit 2bc2026269beb0d7923317f5a4a28ce4d5bbc94c
# Author: Michael Ellerman <mpe@ellerman.id.au>
# Date:   Thu Jul 19 23:36:10 2018 +1000
# 
#     powerpc/mm: Don't report PUDs as memory leaks when using kmemleak
#     
#     Paul Menzel reported that kmemleak was producing reports such as:
#     
#       unreferenced object 0xc0000000f8b80000 (size 16384):
#         comm "init", pid 1, jiffies 4294937416 (age 312.240s)
#         hex dump (first 32 bytes):
#           00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
#           00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
#         backtrace:
#           [<00000000d997deb7>] __pud_alloc+0x80/0x190
#           [<0000000087f2e8a3>] move_page_tables+0xbac/0xdc0
#           [<00000000091e51c2>] shift_arg_pages+0xc0/0x210
#           [<00000000ab88670c>] setup_arg_pages+0x22c/0x2a0
#           [<0000000060871529>] load_elf_binary+0x41c/0x1648
#           [<00000000ecd9d2d4>] search_binary_handler.part.11+0xbc/0x280
#           [<0000000034e0cdd7>] __do_execve_file.isra.13+0x73c/0x940
#           [<000000005f953a6e>] sys_execve+0x58/0x70
#           [<000000009700a858>] system_call+0x5c/0x70
#     
#     Indicating that a PUD was being leaked.
#     
#     However what's really happening is that kmemleak is not able to
#     recognise the references from the PGD to the PUD, because they are not
#     fully qualified pointers.
#     
#     We can confirm that in xmon, eg:
#     
#     Find the task struct for pid 1 "init":
#       0:mon> P
#            task_struct     ->thread.ksp    PID   PPID S  P CMD
#       c0000001fe7c0000 c0000001fe803960      1      0 S 13 systemd
#     
#     Dump virtual address 0 to find the PGD:
#       0:mon> dv 0 c0000001fe7c0000
#       pgd  @ 0xc0000000f8b01000
#     
#     Dump the memory of the PGD:
#       0:mon> d c0000000f8b01000
#       c0000000f8b01000 00000000f8b90000 0000000000000000  |................|
#       c0000000f8b01010 0000000000000000 0000000000000000  |................|
#       c0000000f8b01020 0000000000000000 0000000000000000  |................|
#       c0000000f8b01030 0000000000000000 00000000f8b80000  |................|
#                                         ^^^^^^^^^^^^^^^^
#     
#     There we can see the reference to our supposedly leaked PUD. But
#     because it's missing the leading 0xc, kmemleak won't recognise it.
#     
#     We can confirm it's still in use by translating an address that is
#     mapped via it:
#       0:mon> dv 7fff94000000 c0000001fe7c0000
#       pgd  @ 0xc0000000f8b01000
#       pgdp @ 0xc0000000f8b01038 = 0x00000000f8b80000 <--
#       pudp @ 0xc0000000f8b81ff8 = 0x00000000037c4000
#       pmdp @ 0xc0000000037c5ca0 = 0x00000000fbd89000
#       ptep @ 0xc0000000fbd89000 = 0xc0800001d5ce0386
#       Maps physical address = 0x00000001d5ce0000
#       Flags = Accessed Dirty Read Write
#     
#     The fix is fairly simple. We need to tell kmemleak to ignore PUD
#     allocations and never report them as leaks. We can also tell it not to
#     scan the PGD, because it will never find pointers in there. However it
#     will still notice if we allocate a PGD and then leak it.
#     
#     Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
# < /opt/cross/kisskb/gcc-5.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < git log --format=%s --max-count=1 2bc2026269beb0d7923317f5a4a28ce4d5bbc94c
# < make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-next_tqm8xx_defconfig_powerpc-5.3 CROSS_COMPILE=/opt/cross/kisskb/gcc-5.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  tqm8xx_defconfig
# make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-next_tqm8xx_defconfig_powerpc-5.3 CROSS_COMPILE=/opt/cross/kisskb/gcc-5.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  
/kisskb/src/net/Makefile:24: CC cannot link executables. Skipping bpfilter.
/kisskb/src/net/Makefile:24: CC cannot link executables. Skipping bpfilter.
Completed OK
# rm -rf /kisskb/build/powerpc-next_tqm8xx_defconfig_powerpc-5.3
# Build took: 0:00:36.519946