# git rev-parse -q --verify e3a36eb6dfaeea8175c05d5915dcf0b939be6dab^{commit}
e3a36eb6dfaeea8175c05d5915dcf0b939be6dab
already have revision, skipping fetch
# git checkout -q -f -B kisskb e3a36eb6dfaeea8175c05d5915dcf0b939be6dab
# git clean -qxdf
# < git log -1
# commit e3a36eb6dfaeea8175c05d5915dcf0b939be6dab
# Author: Christoph Hellwig <hch@lst.de>
# Date:   Wed Mar 11 17:07:10 2020 +0100
# 
#     driver code: clarify and fix platform device DMA mask allocation
#     
#     This does three inter-related things to clarify the usage of the
#     platform device dma_mask field. In the process, fix the bug introduced
#     by cdfee5623290 ("driver core: initialize a default DMA mask for
#     platform device") that caused Artem Tashkinov's laptop to not boot with
#     newer Fedora kernels.
#     
#     This does:
#     
#      - First off, rename the field to "platform_dma_mask" to make it
#        greppable.
#     
#        We have way too many different random fields called "dma_mask" in
#        various data structures, where some of them are actual masks, and
#        some of them are just pointers to the mask. And the structures all
#        have pointers to each other, or embed each other inside themselves,
#        and "pdev" sometimes means "platform device" and sometimes it means
#        "PCI device".
#     
#        So to make it clear in the code when you actually use this new field,
#        give it a unique name (it really should be something even more unique
#        like "platform_device_dma_mask", since it's per platform device, not
#        per platform, but that gets old really fast, and this is unique
#        enough in context).
#     
#        To further clarify when the field gets used, initialize it when we
#        actually start using it with the default value.
#     
#      - Then, use this field instead of the random one-off allocation in
#        platform_device_register_full() that is now unnecessary since we now
#        already have a perfectly fine allocation for it in the platform
#        device structure.
#     
#      - The above then allows us to fix the actual bug, where the error path
#        of platform_device_register_full() would unconditionally free the
#        platform device DMA allocation with 'kfree()'.
#     
#        That kfree() was dont regardless of whether the allocation had been
#        done earlier with the (now removed) kmalloc, or whether
#        setup_pdev_dma_masks() had already been used and the dma_mask pointer
#        pointed to the mask that was part of the platform device.
#     
#     It seems most people never triggered the error path, or only triggered
#     it from a call chain that set an explicit pdevinfo->dma_mask value (and
#     thus caused the unnecessary allocation that was "cleaned up" in the
#     error path) before calling platform_device_register_full().
#     
#     Robin Murphy points out that in Artem's case the wdat_wdt driver failed
#     in platform_device_add(), and that was the one that had called
#     platform_device_register_full() with pdevinfo.dma_mask = 0, and would
#     have caused that kfree() of pdev.dma_mask corrupting the heap.
#     
#     A later unrelated kmalloc() then oopsed due to the heap corruption.
#     
#     Fixes: cdfee5623290 ("driver core: initialize a default DMA mask for platform device")
#     Reported-bisected-and-tested-by:  Artem S. Tashkinov <aros@gmx.com>
#     Reviewed-by: Robin Murphy <robin.murphy@arm.com>
#     Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
#     Signed-off-by: Christoph Hellwig <hch@lst.de>
#     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-gcc --version
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-ld --version
# < git log --format=%s --max-count=1 e3a36eb6dfaeea8175c05d5915dcf0b939be6dab
# < make -s -j 48 ARCH=arm O=/kisskb/build/linus_u300_defconfig_arm-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-  u300_defconfig
# < make -s -j 48 ARCH=arm O=/kisskb/build/linus_u300_defconfig_arm-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-  help
# make -s -j 48 ARCH=arm O=/kisskb/build/linus_u300_defconfig_arm-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-  olddefconfig
# make -s -j 48 ARCH=arm O=/kisskb/build/linus_u300_defconfig_arm-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-  
Completed OK
# rm -rf /kisskb/build/linus_u300_defconfig_arm-gcc4.9
# Build took: 0:00:32.029740