kernel/linux.git/init/Kconfig, branch v5.16.1

kbuild: Fix -Wimplicit-fallthrough=5 error for GCC 5.x and 6.x

2021-11-15T02:59:49+00:00

-Wimplicit-fallthrough=5 was under cc-option because it was only available in GCC 7.x and newer so the build is now broken for GCC 5.x and 6.x: gcc: error: unrecognized command line option '-Wimplicit-fallthrough=5'; did you mean '-Wno-fallthrough'? Fix this by moving -Wimplicit-fallthrough=5 under cc-option. Fixes: dee2b702bcf0 ("kconfig: Add support for -Wimplicit-fallthrough") Reported-by: Nathan Chancellor Co-developed-by: Nathan Chancellor Signed-off-by: Nathan Chancellor Signed-off-by: Gustavo A. R. Silva Signed-off-by: Linus Torvalds

kconfig: Add support for -Wimplicit-fallthrough

2021-11-14T21:27:30+00:00

Add Kconfig support for -Wimplicit-fallthrough for both GCC and Clang. The compiler option is under configuration CC_IMPLICIT_FALLTHROUGH, which is enabled by default. Special thanks to Nathan Chancellor who fixed the Clang bug[1][2]. This bugfix only appears in Clang 14.0.0, so older versions still contain the bug and -Wimplicit-fallthrough won't be enabled for them, for now. This concludes a long journey and now we are finally getting rid of the unintentional fallthrough bug-class in the kernel, entirely. :) Link: https://github.com/llvm/llvm-project/commit/9ed4a94d6451046a51ef393cd62f00710820a7e8 [1] Link: https://bugs.llvm.org/show_bug.cgi?id=51094 [2] Link: https://github.com/KSPP/linux/issues/115 Link: https://github.com/ClangBuiltLinux/linux/issues/236 Co-developed-by: Kees Cook Signed-off-by: Kees Cook Co-developed-by: Linus Torvalds Signed-off-by: Linus Torvalds Signed-off-by: Gustavo A. R. Silva Reviewed-by: Nathan Chancellor Tested-by: Nathan Chancellor Signed-off-by: Linus Torvalds

mm: allow only SLUB on PREEMPT_RT

2021-11-11T17:34:35+00:00

Memory allocators may disable interrupts or preemption as part of the allocation and freeing process. For PREEMPT_RT it is important that these sections remain deterministic and short and therefore don't depend on the size of the memory to allocate/ free or the inner state of the algorithm. Until v3.12-RT the SLAB allocator was an option but involved several changes to meet all the requirements. The SLUB design fits better with PREEMPT_RT model and so the SLAB patches were dropped in the 3.12-RT patchset. Comparing the two allocator, SLUB outperformed SLAB in both throughput (time needed to allocate and free memory) and the maximal latency of the system measured with cyclictest during hackbench. SLOB was never evaluated since it was unlikely that it preforms better than SLAB. During a quick test, the kernel crashed with SLOB enabled during boot. Disable SLAB and SLOB on PREEMPT_RT. [bigeasy@linutronix.de: commit description] Link: https://lkml.kernel.org/r/20211015210336.gen3tib33ig5q2md@linutronix.de Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner Signed-off-by: Sebastian Andrzej Siewior Acked-by: Vlastimil Babka Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: disable NUMA_BALANCING_DEFAULT_ENABLED and TRANSPARENT_HUGEPAGE on PREEMPT_RT

2021-11-06T20:30:33+00:00

TRANSPARENT_HUGEPAGE: There are potential non-deterministic delays to an RT thread if a critical memory region is not THP-aligned and a non-RT buffer is located in the same hugepage-aligned region. It's also possible for an unrelated thread to migrate pages belonging to an RT task incurring unexpected page faults due to memory defragmentation even if khugepaged is disabled. Regular HUGEPAGEs are not affected by this can be used. NUMA_BALANCING: There is a non-deterministic delay to mark PTEs PROT_NONE to gather NUMA fault samples, increased page faults of regions even if mlocked and non-deterministic delays when migrating pages. [Mel Gorman worded 99% of the commit description]. Link: https://lore.kernel.org/all/20200304091159.GN3818@techsingularity.net/ Link: https://lore.kernel.org/all/20211026165100.ahz5bkx44lrrw5pt@linutronix.de/ Link: https://lkml.kernel.org/r/20211028143327.hfbxjze7palrpfgp@linutronix.de Signed-off-by: Sebastian Andrzej Siewior Acked-by: Mel Gorman Reviewed-by: David Hildenbrand Cc: Vlastimil Babka Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

kbuild: Only default to -Werror if COMPILE_TEST

2021-09-08T01:47:04+00:00

The cross-product of the kernel's supported toolchains, architectures, and configuration options is large. So large, that it's generally accepted to be infeasible to enumerate and build+test them all (many compile-testers rely on randomly generated configs). Without the possibility to enumerate all possible combinations of toolchains, architectures, and configuration options, it is inevitable that compiler warnings in this space exist. With -Werror, this means that an innumerable set of kernels are now broken, yet had been perfectly usable before (confused compilers, code with warnings unused, or luck). Distributors will necessarily pick a point in the toolchain X arch X config space, and if unlucky, will have a broken build. Granted, those will likely disable CONFIG_WERROR and move on. The kernel's default configuration is unlikely to be suitable for all users, but it's inappropriate to force many users to set CONFIG_WERROR=n. This also holds for CI systems which are focused on runtime testing, where the odd warning in some subsystem will disrupt testing of the rest of the kernel. Many of those runtime-focused CI systems run tests or fuzz the kernel using runtime debugging tools. Runtime testing of different subsystems can proceed in parallel, and potentially uncover serious bugs; halting runtime testing of the entire kernel because of the odd warning (now error) in a subsystem or driver is simply inappropriate. Therefore, runtime-focused CI systems will likely choose CONFIG_WERROR=n as well. The appropriate usecase for -Werror is therefore compile-test focused builds (often done by developers or CI systems). Reflect this in the Kconfig option by making the default value of WERROR match COMPILE_TEST. Signed-off-by: Marco Elver Acked-by: Guenter Roeck Acked-by: Randy Dunlap Reviwed-by: Mark Brown Reviewed-by: Nathan Chancellor Signed-off-by: Linus Torvalds

Enable '-Werror' by default for all kernel builds

2021-09-05T18:24:05+00:00

... but make it a config option so that broken environments can disable it when required. We really should always have a clean build, and will disable specific over-eager warnings as required, if we can't fix them. But while I fairly religiously enforce that in my own tree, it doesn't get enforced by various build robots that don't necessarily report warnings. So this just makes '-Werror' a default compiler flag, but allows people to disable it for their configuration if they have some particular issues. Occasionally, new compiler versions end up enabling new warnings, and it can take a while before we have them fixed (or the warnings disabled if that is what it takes), so the config option allows for that situation. Hopefully this will mean that I get fewer pull requests that have new warnings that were not noticed by various automation we have in place. Knock wood. Signed-off-by: Linus Torvalds

Merge tag 'printk-for-5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

2021-09-02T01:41:13+00:00

Pull printk updates from Petr Mladek: - Optionally, provide an index of possible printk messages via /printk/index/. It can be used when monitoring important kernel messages on a farm of various hosts. The monitor has to be updated when some messages has changed or are not longer available by a newly deployed kernel. - Add printk.console_no_auto_verbose boot parameter. It allows to generate crash dump even with slow consoles in a reasonable time frame. - Remove printk_safe buffers. The messages are always stored directly to the main logbuffer, even in NMI or recursive context. Also it allows to serialize syslog operations by a mutex instead of a spin lock. - Misc clean up and build fixes. * tag 'printk-for-5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux: printk/index: Fix -Wunused-function warning lib/nmi_backtrace: Serialize even messages about idle CPUs printk: Add printk.console_no_auto_verbose boot parameter printk: Remove console_silent() lib/test_scanf: Handle n_bits == 0 in random tests printk: syslog: close window between wait and read printk: convert @syslog_lock to mutex printk: remove NMI tracking printk: remove safe buffers printk: track/limit recursion lib/nmi_backtrace: explicitly serialize banner and regs printk: Move the printk() kerneldoc comment to its new home printk/index: Fix warning about missing prototypes MIPS/asm/printk: Fix build failure caused by printk printk: index: Add indexing support to dev_printk printk: Userspace format indexing support printk: Rework parse_prefix into printk_parse_prefix printk: Straighten out log_flags into printk_info_flags string_helpers: Escape double quotes in escape_special printk/console: Check consistent sequence number when handling race in console_unlock()

Merge branch 'rework/printk_safe-removal' into for-linus

2021-08-30T14:36:10+00:00

printk: remove NMI tracking

2021-07-26T13:09:44+00:00

All NMI contexts are handled the same as the safe context: store the message and defer printing. There is no need to have special NMI context tracking for this. Using in_nmi() is enough. There are several parts of the kernel that are manually calling into the printk NMI context tracking in order to cause general printk deferred printing: arch/arm/kernel/smp.c arch/powerpc/kexec/crash.c kernel/trace/trace.c For arm/kernel/smp.c and powerpc/kexec/crash.c, provide a new function pair printk_deferred_enter/exit that explicitly achieves the same objective. For ftrace, remove the printk context manipulation completely. It was added in commit 03fc7f9c99c1 ("printk/nmi: Prevent deadlock when accessing the main log buffer in NMI"). The purpose was to enforce storing messages directly into the ring buffer even in NMI context. It really should have only modified the behavior in NMI context. There is no need for a special behavior any longer. All messages are always stored directly now. The console deferring is handled transparently in vprintk(). Signed-off-by: John Ogness [pmladek@suse.com: Remove special handling in ftrace.c completely. Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210715193359.25946-5-john.ogness@linutronix.de

printk: Userspace format indexing support

2021-07-19T09:57:48+00:00

We have a number of systems industry-wide that have a subset of their functionality that works as follows: 1. Receive a message from local kmsg, serial console, or netconsole; 2. Apply a set of rules to classify the message; 3. Do something based on this classification (like scheduling a remediation for the machine), rinse, and repeat. As a couple of examples of places we have this implemented just inside Facebook, although this isn't a Facebook-specific problem, we have this inside our netconsole processing (for alarm classification), and as part of our machine health checking. We use these messages to determine fairly important metrics around production health, and it's important that we get them right. While for some kinds of issues we have counters, tracepoints, or metrics with a stable interface which can reliably indicate the issue, in order to react to production issues quickly we need to work with the interface which most kernel developers naturally use when developing: printk. Most production issues come from unexpected phenomena, and as such usually the code in question doesn't have easily usable tracepoints or other counters available for the specific problem being mitigated. We have a number of lines of monitoring defence against problems in production (host metrics, process metrics, service metrics, etc), and where it's not feasible to reliably monitor at another level, this kind of pragmatic netconsole monitoring is essential. As one would expect, monitoring using printk is rather brittle for a number of reasons -- most notably that the message might disappear entirely in a new version of the kernel, or that the message may change in some way that the regex or other classification methods start to silently fail. One factor that makes this even harder is that, under normal operation, many of these messages are never expected to be hit. For example, there may be a rare hardware bug which one wants to detect if it was to ever happen again, but its recurrence is not likely or anticipated. This precludes using something like checking whether the printk in question was printed somewhere fleetwide recently to determine whether the message in question is still present or not, since we don't anticipate that it should be printed anywhere, but still need to monitor for its future presence in the long-term. This class of issue has happened on a number of occasions, causing unhealthy machines with hardware issues to remain in production for longer than ideal. As a recent example, some monitoring around blk_update_request fell out of date and caused semi-broken machines to remain in production for longer than would be desirable. Searching through the codebase to find the message is also extremely fragile, because many of the messages are further constructed beyond their callsite (eg. btrfs_printk and other module-specific wrappers, each with their own functionality). Even if they aren't, guessing the format and formulation of the underlying message based on the aesthetics of the message emitted is not a recipe for success at scale, and our previous issues with fleetwide machine health checking demonstrate as much. This provides a solution to the issue of silently changed or deleted printks: we record pointers to all printk format strings known at compile time into a new .printk_index section, both in vmlinux and modules. At runtime, this can then be iterated by looking at /printk/index/, which emits the following format, both readable by humans and able to be parsed by machines: $ head -1 vmlinux; shuf -n 5 vmlinux # filename:line function "format" <5> block/blk-settings.c:661 disk_stack_limits "%s: Warning: Device %s is misaligned\n" <4> kernel/trace/trace.c:8296 trace_create_file "Could not create tracefs '%s' entry\n" <6> arch/x86/kernel/hpet.c:144 _hpet_print_config "hpet: %s(%d):\n" <6> init/do_mounts.c:605 prepare_namespace "Waiting for root device %s...\n" <6> drivers/acpi/osl.c:1410 acpi_no_auto_serialize_setup "ACPI: auto-serialization disabled\n" This mitigates the majority of cases where we have a highly-specific printk which we want to match on, as we can now enumerate and check whether the format changed or the printk callsite disappeared entirely in userspace. This allows us to catch changes to printks we monitor earlier and decide what to do about it before it becomes problematic. There is no additional runtime cost for printk callers or printk itself, and the assembly generated is exactly the same. Signed-off-by: Chris Down Cc: Petr Mladek Cc: Jessica Yu Cc: Sergey Senozhatsky Cc: John Ogness Cc: Steven Rostedt Cc: Greg Kroah-Hartman Cc: Johannes Weiner Cc: Kees Cook Reviewed-by: Petr Mladek Tested-by: Petr Mladek Reported-by: kernel test robot Acked-by: Andy Shevchenko Acked-by: Jessica Yu # for module.{c,h} Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/e42070983637ac5e384f17fbdbe86d19c7b212a5.1623775748.git.chris@chrisdown.name