# git rev-parse -q --verify a4d63c3732f1a0c91abcf5b7f32b4ef7dcd82025^{commit}
a4d63c3732f1a0c91abcf5b7f32b4ef7dcd82025
already have revision, skipping fetch
# git checkout -q -f -B kisskb a4d63c3732f1a0c91abcf5b7f32b4ef7dcd82025
# git clean -qxdf
# < git log -1
# commit a4d63c3732f1a0c91abcf5b7f32b4ef7dcd82025
# Author: Jason A. Donenfeld <Jason@zx2c4.com>
# Date:   Mon Sep 28 12:35:07 2020 +0200
# 
#     mm: do not rely on mm == current->mm in __get_user_pages_locked
#     
#     It seems likely this block was pasted from internal_get_user_pages_fast,
#     which is not passed an mm struct and therefore uses current's.  But
#     __get_user_pages_locked is passed an explicit mm, and current->mm is not
#     always valid. This was hit when being called from i915, which uses:
#     
#       pin_user_pages_remote->
#         __get_user_pages_remote->
#           __gup_longterm_locked->
#             __get_user_pages_locked
#     
#     Before, this would lead to an OOPS:
#     
#       BUG: kernel NULL pointer dereference, address: 0000000000000064
#       #PF: supervisor write access in kernel mode
#       #PF: error_code(0x0002) - not-present page
#       CPU: 10 PID: 1431 Comm: kworker/u33:1 Tainted: P S   U     O      5.9.0-rc7+ #140
#       Hardware name: LENOVO 20QTCTO1WW/20QTCTO1WW, BIOS N2OET47W (1.34 ) 08/06/2020
#       Workqueue: i915-userptr-acquire __i915_gem_userptr_get_pages_worker [i915]
#       RIP: 0010:__get_user_pages_remote+0xd7/0x310
#       Call Trace:
#        __i915_gem_userptr_get_pages_worker+0xc8/0x260 [i915]
#        process_one_work+0x1ca/0x390
#        worker_thread+0x48/0x3c0
#        kthread+0x114/0x130
#        ret_from_fork+0x1f/0x30
#       CR2: 0000000000000064
#     
#     This commit fixes the problem by using the mm pointer passed to the
#     function rather than the bogus one in current.
#     
#     Fixes: 008cfe4418b3 ("mm: Introduce mm_struct.has_pinned")
#     Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
#     Reported-by: Harald Arnesen <harald@skogtun.org>
#     Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
#     Reviewed-by: Peter Xu <peterx@redhat.com>
#     Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
#     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version
# < git log --format=%s --max-count=1 a4d63c3732f1a0c91abcf5b7f32b4ef7dcd82025
# < make -s -j 24 ARCH=powerpc O=/kisskb/build/linus_44x_currituck_defconfig_powerpc-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-  44x/currituck_defconfig
# < make -s -j 24 ARCH=powerpc O=/kisskb/build/linus_44x_currituck_defconfig_powerpc-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-  help
# make -s -j 24 ARCH=powerpc O=/kisskb/build/linus_44x_currituck_defconfig_powerpc-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-  olddefconfig
# make -s -j 24 ARCH=powerpc O=/kisskb/build/linus_44x_currituck_defconfig_powerpc-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-  
/kisskb/src/block/genhd.c: In function 'diskstats_show':
/kisskb/src/block/genhd.c:1667:1: warning: the frame size of 1168 bytes is larger than 1024 bytes [-Wframe-larger-than=]
 }
 ^
Completed OK
# rm -rf /kisskb/build/linus_44x_currituck_defconfig_powerpc-gcc4.9
# Build took: 0:01:22.061201