# git rev-parse -q --verify 574823bfab82d9d8fa47f422778043fbb4b4f50e^{commit}
574823bfab82d9d8fa47f422778043fbb4b4f50e
already have revision, skipping fetch
# git checkout -q -f -B kisskb 574823bfab82d9d8fa47f422778043fbb4b4f50e
# git clean -qxdf
# < git log -1
# commit 574823bfab82d9d8fa47f422778043fbb4b4f50e
# Author: Linus Torvalds <torvalds@linux-foundation.org>
# Date:   Sat Jan 5 17:50:59 2019 -0800
# 
#     Change mincore() to count "mapped" pages rather than "cached" pages
#     
#     The semantics of what "in core" means for the mincore() system call are
#     somewhat unclear, but Linux has always (since 2.3.52, which is when
#     mincore() was initially done) treated it as "page is available in page
#     cache" rather than "page is mapped in the mapping".
#     
#     The problem with that traditional semantic is that it exposes a lot of
#     system cache state that it really probably shouldn't, and that users
#     shouldn't really even care about.
#     
#     So let's try to avoid that information leak by simply changing the
#     semantics to be that mincore() counts actual mapped pages, not pages
#     that might be cheaply mapped if they were faulted (note the "might be"
#     part of the old semantics: being in the cache doesn't actually guarantee
#     that you can access them without IO anyway, since things like network
#     filesystems may have to revalidate the cache before use).
#     
#     In many ways the old semantics were somewhat insane even aside from the
#     information leak issue.  From the very beginning (and that beginning is
#     a long time ago: 2.3.52 was released in March 2000, I think), the code
#     had a comment saying
#     
#       Later we can get more picky about what "in core" means precisely.
#     
#     and this is that "later".  Admittedly it is much later than is really
#     comfortable.
#     
#     NOTE! This is a real semantic change, and it is for example known to
#     change the output of "fincore", since that program literally does a
#     mmmap without populating it, and then doing "mincore()" on that mapping
#     that doesn't actually have any pages in it.
#     
#     I'm hoping that nobody actually has any workflow that cares, and the
#     info leak is real.
#     
#     We may have to do something different if it turns out that people have
#     valid reasons to want the old semantics, and if we can limit the
#     information leak sanely.
#     
#     Cc: Kevin Easton <kevin@guarana.org>
#     Cc: Jiri Kosina <jikos@kernel.org>
#     Cc: Masatake YAMATO <yamato@redhat.com>
#     Cc: Andrew Morton <akpm@linux-foundation.org>
#     Cc: Greg KH <gregkh@linuxfoundation.org>
#     Cc: Peter Zijlstra <peterz@infradead.org>
#     Cc: Michal Hocko <mhocko@suse.com>
#     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
# < /opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-gcc --version
# < /opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-ld --version
# < git log --format=%s --max-count=1 574823bfab82d9d8fa47f422778043fbb4b4f50e
# < make -s -j 10 ARCH=powerpc O=/kisskb/build/linus_powerpc-allnoconfig_powerpc CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-  allnoconfig
# make -s -j 10 ARCH=powerpc O=/kisskb/build/linus_powerpc-allnoconfig_powerpc CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-  
/kisskb/src/kernel/printk/printk.c: In function 'devkmsg_sysctl_set_loglvl':
/kisskb/src/kernel/printk/printk.c:186:16: warning: 'old' may be used uninitialized in this function [-Wuninitialized]
Completed OK
# rm -rf /kisskb/build/linus_powerpc-allnoconfig_powerpc
# Build took: 0:00:14.688129