Buildresult: linus/nds32-allyesconfig/nds32le-gcc8 built on Jul 31 2021, 10:13

kisskb

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Status:	OK
Date/Time:	Jul 31 2021, 10:13
Duration:	0:14:04.507797
Builder:	ka1
Revision:	pipe: make pipe writes always wake up readers (`3a34b13a88caeb2800ab44a4918f230041b37dd9)`
Target:	linus/nds32-allyesconfig/nds32le-gcc8
Branch:	linus
Compiler:	nds32le-gcc8 (nds32le-linux-gcc (GCC) 8.1.0 / GNU ld (GNU Binutils) 2.30.51.20180307)
Config:	allyesconfig (download)
Log:	Download original Possible warnings (7) <stdin>:1515:2: warning: #warning syscall clone3 not implemented [-Wcpp] arch/nds32/kernel/setup.c:247:26: warning: unused variable 'region' [-Wunused-variable] kernel/trace/trace_osnoise.c:1461:8: warning: 'main' is usually a function [-Wmain] drivers/input/joystick/analog.c:160:2: warning: #warning Precise timer not defined for this architecture. [-Wcpp] #warning Precise timer not defined for this architecture. WARNING: modpost: EXPORT symbol "copy_page" [vmlinux] version ... WARNING: modpost: EXPORT symbol "clear_page" [vmlinux] version ... Full Log # git rev-parse -q --verify 3a34b13a88caeb2800ab44a4918f230041b37dd9^{commit} 3a34b13a88caeb2800ab44a4918f230041b37dd9 already have revision, skipping fetch # git checkout -q -f -B kisskb 3a34b13a88caeb2800ab44a4918f230041b37dd9 # git clean -qxdf # < git log -1 # commit 3a34b13a88caeb2800ab44a4918f230041b37dd9 # Author: Linus Torvalds <torvalds@linux-foundation.org> # Date: Fri Jul 30 15:42:34 2021 -0700 # # pipe: make pipe writes always wake up readers # # Since commit 1b6b26ae7053 ("pipe: fix and clarify pipe write wakeup # logic") we have sanitized the pipe write logic, and would only try to # wake up readers if they needed it. # # In particular, if the pipe already had data in it before the write, # there was no point in trying to wake up a reader, since any existing # readers must have been aware of the pre-existing data already. Doing # extraneous wakeups will only cause potential thundering herd problems. # # However, it turns out that some Android libraries have misused the EPOLL # interface, and expected "edge triggered" be to "any new write will # trigger it". Even if there was no edge in sight. # # Quoting Sandeep Patil: # "The commit 1b6b26ae7053 ('pipe: fix and clarify pipe write wakeup # logic') changed pipe write logic to wakeup readers only if the pipe # was empty at the time of write. However, there are libraries that # relied upon the older behavior for notification scheme similar to # what's described in [1] # # One such library 'realm-core'[2] is used by numerous Android # applications. The library uses a similar notification mechanism as GNU # Make but it never drains the pipe until it is full. When Android moved # to v5.10 kernel, all applications using this library stopped working. # # The library has since been fixed[3] but it will be a while before all # applications incorporate the updated library" # # Our regression rule for the kernel is that if applications break from # new behavior, it's a regression, even if it was because the application # did something patently wrong. Also note the original report [4] by # Michal Kerrisk about a test for this epoll behavior - but at that point # we didn't know of any actual broken use case. # # So add the extraneous wakeup, to approximate the old behavior. # # [ I say "approximate", because the exact old behavior was to do a wakeup # not for each write(), but for each pipe buffer chunk that was filled # in. The behavior introduced by this change is not that - this is just # "every write will cause a wakeup, whether necessary or not", which # seems to be sufficient for the broken library use. ] # # It's worth noting that this adds the extraneous wakeup only for the # write side, while the read side still considers the "edge" to be purely # about reading enough from the pipe to allow further writes. # # See commit f467a6a66419 ("pipe: fix and clarify pipe read wakeup logic") # for the pipe read case, which remains that "only wake up if the pipe was # full, and we read something from it". # # Link: https://lore.kernel.org/lkml/CAHk-=wjeG0q1vgzu4iJhW5juPkTsjTYmiqiMUYAebWW+0bam6w@mail.gmail.com/ [1] # Link: https://github.com/realm/realm-core [2] # Link: https://github.com/realm/realm-core/issues/4666 [3] # Link: https://lore.kernel.org/lkml/CAKgNAkjMBGeAwF=2MKK758BhxvW58wYTgYKB2V-gY1PwXxrH+Q@mail.gmail.com/ [4] # Link: https://lore.kernel.org/lkml/20210729222635.2937453-1-sspatil@android.com/ # Reported-by: Sandeep Patil <sspatil@android.com> # Cc: Michael Kerrisk <mtk.manpages@gmail.com> # Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> # < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/nds32le-linux/bin/nds32le-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/nds32le-linux/bin/nds32le-linux-ld --version # < git log --format=%s --max-count=1 3a34b13a88caeb2800ab44a4918f230041b37dd9 # < make -s -j 48 ARCH=nds32 O=/kisskb/build/linus_nds32-allyesconfig_nds32le-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/nds32le-linux/bin/nds32le-linux- allyesconfig # < make -s -j 48 ARCH=nds32 O=/kisskb/build/linus_nds32-allyesconfig_nds32le-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/nds32le-linux/bin/nds32le-linux- help # make -s -j 48 ARCH=nds32 O=/kisskb/build/linus_nds32-allyesconfig_nds32le-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/nds32le-linux/bin/nds32le-linux- olddefconfig # make -s -j 48 ARCH=nds32 O=/kisskb/build/linus_nds32-allyesconfig_nds32le-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/nds32le-linux/bin/nds32le-linux- <stdin>:1515:2: warning: #warning syscall clone3 not implemented [-Wcpp] /kisskb/src/arch/nds32/kernel/setup.c: In function 'setup_memory': /kisskb/src/arch/nds32/kernel/setup.c:247:26: warning: unused variable 'region' [-Wunused-variable] struct memblock_region region; ^~~~~~ /kisskb/src/kernel/trace/trace_osnoise.c: In function 'start_kthread': /kisskb/src/kernel/trace/trace_osnoise.c:1461:8: warning: 'main' is usually a function [-Wmain] void main = osnoise_main; ^~~~ /kisskb/src/drivers/input/joystick/analog.c:160:2: warning: #warning Precise timer not defined for this architecture. [-Wcpp] #warning Precise timer not defined for this architecture. ^~~~~~~ WARNING: modpost: EXPORT symbol "copy_page" [vmlinux] version ... Is "copy_page" prototyped in <asm/asm-prototypes.h>? WARNING: modpost: EXPORT symbol "clear_page" [vmlinux] version ... Is "clear_page" prototyped in <asm/asm-prototypes.h>? Completed OK # rm -rf /kisskb/build/linus_nds32-allyesconfig_nds32le-gcc8 # Build took: 0:14:04.507797

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