# 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 # 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 # Cc: Michael Kerrisk # Signed-off-by: Linus Torvalds # < /opt/cross/kisskb/fe-x86-64-core-i7-2017.05/bin/x86_64-linux-gcc --version # < /opt/cross/kisskb/fe-x86-64-core-i7-2017.05/bin/x86_64-linux-ld --version # < git log --format=%s --max-count=1 3a34b13a88caeb2800ab44a4918f230041b37dd9 # < make -s -j 48 ARCH=um O=/kisskb/build/linus_um-allmodconfig_um-x86_64 CROSS_COMPILE=/opt/cross/kisskb/fe-x86-64-core-i7-2017.05/bin/x86_64-linux- SUBARCH=x86_64 allmodconfig # Added to kconfig CONFIG_STANDALONE=y # Added to kconfig CONFIG_KCOV=n # Added to kconfig CONFIG_GCC_PLUGINS=n # Added to kconfig CONFIG_GCC_PLUGIN_CYC_COMPLEXITY=n # Added to kconfig CONFIG_GCC_PLUGIN_SANCOV=n # Added to kconfig CONFIG_GCC_PLUGIN_LATENT_ENTROPY=n # Added to kconfig CONFIG_GCC_PLUGIN_STRUCTLEAK=n # Added to kconfig CONFIG_GCC_PLUGIN_RANDSTRUCT=n # Added to kconfig CONFIG_UML_NET=n # Added to kconfig CONFIG_UML_NET_ETHERTAP=n # Added to kconfig CONFIG_UML_NET_TUNTAP=n # Added to kconfig CONFIG_UML_NET_SLIP=n # Added to kconfig CONFIG_UML_NET_DAEMON=n # Added to kconfig CONFIG_UML_NET_VDE=n # Added to kconfig CONFIG_UML_NET_MCAST=n # Added to kconfig CONFIG_UML_NET_PCAP=n # Added to kconfig CONFIG_UML_NET_SLIRP=n # Added to kconfig CONFIG_GCOV_KERNEL=n # Added to kconfig CONFIG_DEBUG_INFO_BTF=n # Added to kconfig CONFIG_BPF_PRELOAD=n # < make -s -j 48 ARCH=um O=/kisskb/build/linus_um-allmodconfig_um-x86_64 CROSS_COMPILE=/opt/cross/kisskb/fe-x86-64-core-i7-2017.05/bin/x86_64-linux- SUBARCH=x86_64 help # make -s -j 48 ARCH=um O=/kisskb/build/linus_um-allmodconfig_um-x86_64 CROSS_COMPILE=/opt/cross/kisskb/fe-x86-64-core-i7-2017.05/bin/x86_64-linux- SUBARCH=x86_64 olddefconfig .config:11594:warning: override: reassigning to symbol GCC_PLUGIN_SANCOV .config:11597:warning: override: reassigning to symbol GCC_PLUGIN_RANDSTRUCT .config:11599:warning: override: reassigning to symbol UML_NET_ETHERTAP .config:11601:warning: override: reassigning to symbol UML_NET_SLIP .config:11604:warning: override: reassigning to symbol UML_NET_MCAST .config:11606:warning: override: reassigning to symbol UML_NET_SLIRP # make -s -j 48 ARCH=um O=/kisskb/build/linus_um-allmodconfig_um-x86_64 CROSS_COMPILE=/opt/cross/kisskb/fe-x86-64-core-i7-2017.05/bin/x86_64-linux- SUBARCH=x86_64 /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/video/fbdev/riva/fbdev.c: In function 'rivafb_probe': /kisskb/src/drivers/video/fbdev/riva/fbdev.c:2059:11: warning: passing argument 1 of 'iounmap' discards 'volatile' qualifier from pointer target type [-Wdiscarded-qualifiers] iounmap(default_par->riva.PRAMIN); ^ In file included from /kisskb/src/arch/um/include/asm/io.h:7:0, from /kisskb/src/include/linux/io.h:13, from /kisskb/src/include/linux/irq.h:20, from /kisskb/src/include/asm-generic/hardirq.h:17, from /kisskb/src/arch/um/include/asm/hardirq.h:5, from /kisskb/src/include/linux/hardirq.h:11, from /kisskb/src/include/linux/interrupt.h:11, from /kisskb/src/include/linux/trace_recursion.h:5, from /kisskb/src/include/linux/ftrace.h:10, from /kisskb/src/include/linux/kprobes.h:29, from /kisskb/src/include/linux/kgdb.h:19, from /kisskb/src/include/linux/fb.h:5, from /kisskb/src/drivers/video/fbdev/riva/fbdev.c:39: /kisskb/src/include/asm-generic/logic_io.h:36:17: note: expected 'void *' but argument is of type 'volatile U032 * {aka volatile unsigned int *}' #define iounmap iounmap ^ /kisskb/src/include/asm-generic/logic_io.h:37:6: note: in expansion of macro 'iounmap' void iounmap(void __iomem *addr); ^ /kisskb/src/drivers/video/fbdev/riva/fbdev.c: In function 'rivafb_remove': /kisskb/src/drivers/video/fbdev/riva/fbdev.c:2092:11: warning: passing argument 1 of 'iounmap' discards 'volatile' qualifier from pointer target type [-Wdiscarded-qualifiers] iounmap(par->riva.PRAMIN); ^ In file included from /kisskb/src/arch/um/include/asm/io.h:7:0, from /kisskb/src/include/linux/io.h:13, from /kisskb/src/include/linux/irq.h:20, from /kisskb/src/include/asm-generic/hardirq.h:17, from /kisskb/src/arch/um/include/asm/hardirq.h:5, from /kisskb/src/include/linux/hardirq.h:11, from /kisskb/src/include/linux/interrupt.h:11, from /kisskb/src/include/linux/trace_recursion.h:5, from /kisskb/src/include/linux/ftrace.h:10, from /kisskb/src/include/linux/kprobes.h:29, from /kisskb/src/include/linux/kgdb.h:19, from /kisskb/src/include/linux/fb.h:5, from /kisskb/src/drivers/video/fbdev/riva/fbdev.c:39: /kisskb/src/include/asm-generic/logic_io.h:36:17: note: expected 'void *' but argument is of type 'volatile U032 * {aka volatile unsigned int *}' #define iounmap iounmap ^ /kisskb/src/include/asm-generic/logic_io.h:37:6: note: in expansion of macro 'iounmap' void iounmap(void __iomem *addr); ^ /kisskb/src/drivers/video/fbdev/nvidia/nvidia.c: In function 'nvidiafb_probe': /kisskb/src/drivers/video/fbdev/nvidia/nvidia.c:1414:10: warning: passing argument 1 of 'iounmap' discards 'volatile' qualifier from pointer target type [-Wdiscarded-qualifiers] iounmap(par->REGS); ^ In file included from /kisskb/src/arch/um/include/asm/io.h:7:0, from /kisskb/src/include/linux/io.h:13, from /kisskb/src/include/linux/irq.h:20, from /kisskb/src/include/asm-generic/hardirq.h:17, from /kisskb/src/arch/um/include/asm/hardirq.h:5, from /kisskb/src/include/linux/hardirq.h:11, from /kisskb/src/include/linux/interrupt.h:11, from /kisskb/src/include/linux/trace_recursion.h:5, from /kisskb/src/include/linux/ftrace.h:10, from /kisskb/src/include/linux/kprobes.h:29, from /kisskb/src/include/linux/kgdb.h:19, from /kisskb/src/include/linux/fb.h:5, from /kisskb/src/drivers/video/fbdev/nvidia/nvidia.c:19: /kisskb/src/include/asm-generic/logic_io.h:36:17: note: expected 'void *' but argument is of type 'volatile u32 * {aka volatile unsigned int *}' #define iounmap iounmap ^ /kisskb/src/include/asm-generic/logic_io.h:37:6: note: in expansion of macro 'iounmap' void iounmap(void __iomem *addr); ^ /kisskb/src/drivers/video/fbdev/nvidia/nvidia.c: In function 'nvidiafb_remove': /kisskb/src/drivers/video/fbdev/nvidia/nvidia.c:1439:10: warning: passing argument 1 of 'iounmap' discards 'volatile' qualifier from pointer target type [-Wdiscarded-qualifiers] iounmap(par->REGS); ^ In file included from /kisskb/src/arch/um/include/asm/io.h:7:0, from /kisskb/src/include/linux/io.h:13, from /kisskb/src/include/linux/irq.h:20, from /kisskb/src/include/asm-generic/hardirq.h:17, from /kisskb/src/arch/um/include/asm/hardirq.h:5, from /kisskb/src/include/linux/hardirq.h:11, from /kisskb/src/include/linux/interrupt.h:11, from /kisskb/src/include/linux/trace_recursion.h:5, from /kisskb/src/include/linux/ftrace.h:10, from /kisskb/src/include/linux/kprobes.h:29, from /kisskb/src/include/linux/kgdb.h:19, from /kisskb/src/include/linux/fb.h:5, from /kisskb/src/drivers/video/fbdev/nvidia/nvidia.c:19: /kisskb/src/include/asm-generic/logic_io.h:36:17: note: expected 'void *' but argument is of type 'volatile u32 * {aka volatile unsigned int *}' #define iounmap iounmap ^ /kisskb/src/include/asm-generic/logic_io.h:37:6: note: in expansion of macro 'iounmap' void iounmap(void __iomem *addr); ^ /kisskb/src/drivers/pci/controller/vmd.c:116:21: error: field 'sysdata' has incomplete type struct pci_sysdata sysdata; ^ /kisskb/src/drivers/pci/controller/vmd.c: In function 'vmd_compose_msi_msg': /kisskb/src/drivers/pci/controller/vmd.c:150:20: error: 'X86_MSI_BASE_ADDRESS_HIGH' undeclared (first use in this function) msg->address_hi = X86_MSI_BASE_ADDRESS_HIGH; ^ /kisskb/src/drivers/pci/controller/vmd.c:150:20: note: each undeclared identifier is reported only once for each function it appears in /kisskb/src/drivers/pci/controller/vmd.c:151:19: error: 'arch_msi_msg_addr_lo_t {aka struct arch_msi_msg_addr_lo}' has no member named 'base_address' msg->arch_addr_lo.base_address = X86_MSI_BASE_ADDRESS_LOW; ^ /kisskb/src/drivers/pci/controller/vmd.c:151:35: error: 'X86_MSI_BASE_ADDRESS_LOW' undeclared (first use in this function) msg->arch_addr_lo.base_address = X86_MSI_BASE_ADDRESS_LOW; ^ /kisskb/src/drivers/pci/controller/vmd.c:152:19: error: 'arch_msi_msg_addr_lo_t {aka struct arch_msi_msg_addr_lo}' has no member named 'destid_0_7' msg->arch_addr_lo.destid_0_7 = index_from_irqs(vmd, irq); ^ /kisskb/src/drivers/pci/controller/vmd.c: In function 'vmd_enable_domain': /kisskb/src/drivers/pci/controller/vmd.c:700:4: error: dereferencing pointer to incomplete type 'struct pci_sysdata' sd->vmd_dev = vmd->dev; ^ /kisskb/src/drivers/pci/controller/vmd.c: In function 'vmd_from_bus': /kisskb/src/drivers/pci/controller/vmd.c:127:1: error: control reaches end of non-void function [-Werror=return-type] } ^ cc1: some warnings being treated as errors make[4]: *** [/kisskb/src/scripts/Makefile.build:271: drivers/pci/controller/vmd.o] Error 1 make[4]: *** Waiting for unfinished jobs.... make[3]: *** [/kisskb/src/scripts/Makefile.build:514: drivers/pci/controller] Error 2 make[2]: *** [/kisskb/src/scripts/Makefile.build:514: drivers/pci] Error 2 make[2]: *** Waiting for unfinished jobs.... make[1]: *** [/kisskb/src/Makefile:1842: drivers] Error 2 make: *** [Makefile:220: __sub-make] Error 2 Command 'make -s -j 48 ARCH=um O=/kisskb/build/linus_um-allmodconfig_um-x86_64 CROSS_COMPILE=/opt/cross/kisskb/fe-x86-64-core-i7-2017.05/bin/x86_64-linux- SUBARCH=x86_64 ' returned non-zero exit status 2 # rm -rf /kisskb/build/linus_um-allmodconfig_um-x86_64 # Build took: 0:04:36.266667