# git rev-parse -q --verify 980411a4d1bb925d28cd9e8d8301dc982ece788d^{commit}
980411a4d1bb925d28cd9e8d8301dc982ece788d
already have revision, skipping fetch
# git checkout -q -f -B kisskb 980411a4d1bb925d28cd9e8d8301dc982ece788d
# git clean -qxdf
# < git log -1
# commit 980411a4d1bb925d28cd9e8d8301dc982ece788d
# Author: Michael Ellerman <mpe@ellerman.id.au>
# Date:   Fri Dec 16 12:43:12 2022 +1100
# 
#     powerpc/code-patching: Fix oops with DEBUG_VM enabled
#     
#     Nathan reported that the new per-cpu mm patching oopses if DEBUG_VM is
#     enabled:
#     
#       ------------[ cut here ]------------
#       kernel BUG at arch/powerpc/mm/pgtable.c:333!
#       Oops: Exception in kernel mode, sig: 5 [#1]
#       LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA PowerNV
#       Modules linked in:
#       CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.1.0-rc2+ #1
#       Hardware name: IBM PowerNV (emulated by qemu) POWER9 0x4e1200 opal:v7.0 PowerNV
#       ...
#       NIP assert_pte_locked+0x180/0x1a0
#       LR  assert_pte_locked+0x170/0x1a0
#       Call Trace:
#         0x60000000 (unreliable)
#         patch_instruction+0x618/0x6d0
#         arch_prepare_kprobe+0xfc/0x2d0
#         register_kprobe+0x520/0x7c0
#         arch_init_kprobes+0x28/0x3c
#         init_kprobes+0x108/0x184
#         do_one_initcall+0x60/0x2e0
#         kernel_init_freeable+0x1f0/0x3e0
#         kernel_init+0x34/0x1d0
#         ret_from_kernel_thread+0x5c/0x64
#     
#     It's caused by the assert_spin_locked() failing in assert_pte_locked().
#     The assert fails because the PTE was unlocked in text_area_cpu_up_mm(),
#     and never relocked.
#     
#     The PTE page shouldn't be freed, the patching_mm is only used for
#     patching on this CPU, only that single PTE is ever mapped, and it's only
#     unmapped at CPU offline.
#     
#     In fact assert_pte_locked() has a special case to ignore init_mm
#     entirely, and the patching_mm is more-or-less like init_mm, so possibly
#     the check could be skipped for patching_mm too.
#     
#     But for now be conservative, and use the proper PTE accessors at
#     patching time, so that the PTE lock is held while the PTE is used. That
#     also avoids the warning in assert_pte_locked().
#     
#     With that it's no longer necessary to save the PTE in
#     cpu_patching_context for the mm_patch_enabled() case.
#     
#     Fixes: c28c15b6d28a ("powerpc/code-patching: Use temporary mm for Radix MMU")
#     Reported-by: Nathan Chancellor <nathan@kernel.org>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
#     Link: https://lore.kernel.org/r/20221216125913.990972-1-mpe@ellerman.id.au
# < /opt/cross/kisskb/korg/gcc-12.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-12.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version
# < git log --format=%s --max-count=1 980411a4d1bb925d28cd9e8d8301dc982ece788d
# < make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-next_ppc64_defconfig_powerpc-gcc12 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-12.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  ppc64_defconfig
# < make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-next_ppc64_defconfig_powerpc-gcc12 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-12.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  help
# make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-next_ppc64_defconfig_powerpc-gcc12 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-12.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  olddefconfig
# make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-next_ppc64_defconfig_powerpc-gcc12 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-12.2.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  
Completed OK
# rm -rf /kisskb/build/powerpc-next_ppc64_defconfig_powerpc-gcc12
# Build took: 0:03:25.769510