aboutsummaryrefslogtreecommitdiffstats
path: root/Makefile (unfollow)
AgeCommit message (Collapse)AuthorFilesLines
2015-03-29Linux 4.0-rc6Linus Torvalds1-1/+1
2015-03-22Linux 4.0-rc5Linus Torvalds1-1/+1
2015-03-15Linux 4.0-rc4Linus Torvalds1-1/+1
2015-03-08Linux 4.0-rc3Linus Torvalds1-1/+1
2015-03-03Linux 4.0-rc2Linus Torvalds1-1/+1
2015-02-22Linux 4.0-rc1Linus Torvalds1-4/+4
.. after extensive statistical analysis of my G+ polling, I've come to the inescapable conclusion that internet polls are bad. Big surprise. But "Hurr durr I'ma sheep" trounced "I like online polls" by a 62-to-38% margin, in a poll that people weren't even supposed to participate in. Who can argue with solid numbers like that? 5,796 votes from people who can't even follow the most basic directions? In contrast, "v4.0" beat out "v3.20" by a slimmer margin of 56-to-44%, but with a total of 29,110 votes right now. Now, arguably, that vote spread is only about 3,200 votes, which is less than the almost six thousand votes that the "please ignore" poll got, so it could be considered noise. But hey, I asked, so I'll honor the votes.
2015-02-17scripts/gdb: add infrastructureJan Kiszka1-1/+4
This provides the basic infrastructure to load kernel-specific python helper scripts when debugging the kernel in gdb. The loading mechanism is based on gdb loading for <objfile>-gdb.py when opening <objfile>. Therefore, this places a corresponding link to the main helper script into the output directory that contains vmlinux. The main scripts will pull in submodules containing Linux specific gdb commands and functions. To avoid polluting the source directory with compiled python modules, we link to them from the object directory. Due to gdb.parse_and_eval and string redirection for gdb.execute, we depend on gdb >= 7.2. This feature is enabled via CONFIG_GDB_SCRIPTS. Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com> Acked-by: Michal Marek <mmarek@suse.cz> [kbuild stuff] Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Jason Wessel <jason.wessel@windriver.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: Ben Widawsky <ben@bwidawsk.net> Cc: Borislav Petkov <bp@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-13kasan: add kernel address sanitizer infrastructureAndrey Ryabinin1-1/+2
Kernel Address sanitizer (KASan) is a dynamic memory error detector. It provides fast and comprehensive solution for finding use-after-free and out-of-bounds bugs. KASAN uses compile-time instrumentation for checking every memory access, therefore GCC > v4.9.2 required. v4.9.2 almost works, but has issues with putting symbol aliases into the wrong section, which breaks kasan instrumentation of globals. This patch only adds infrastructure for kernel address sanitizer. It's not available for use yet. The idea and some code was borrowed from [1]. Basic idea: The main idea of KASAN is to use shadow memory to record whether each byte of memory is safe to access or not, and use compiler's instrumentation to check the shadow memory on each memory access. Address sanitizer uses 1/8 of the memory addressable in kernel for shadow memory and uses direct mapping with a scale and offset to translate a memory address to its corresponding shadow address. Here is function to translate address to corresponding shadow address: unsigned long kasan_mem_to_shadow(unsigned long addr) { return (addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET; } where KASAN_SHADOW_SCALE_SHIFT = 3. So for every 8 bytes there is one corresponding byte of shadow memory. The following encoding used for each shadow byte: 0 means that all 8 bytes of the corresponding memory region are valid for access; k (1 <= k <= 7) means that the first k bytes are valid for access, and other (8 - k) bytes are not; Any negative value indicates that the entire 8-bytes are inaccessible. Different negative values used to distinguish between different kinds of inaccessible memory (redzones, freed memory) (see mm/kasan/kasan.h). To be able to detect accesses to bad memory we need a special compiler. Such compiler inserts a specific function calls (__asan_load*(addr), __asan_store*(addr)) before each memory access of size 1, 2, 4, 8 or 16. These functions check whether memory region is valid to access or not by checking corresponding shadow memory. If access is not valid an error printed. Historical background of the address sanitizer from Dmitry Vyukov: "We've developed the set of tools, AddressSanitizer (Asan), ThreadSanitizer and MemorySanitizer, for user space. We actively use them for testing inside of Google (continuous testing, fuzzing, running prod services). To date the tools have found more than 10'000 scary bugs in Chromium, Google internal codebase and various open-source projects (Firefox, OpenSSL, gcc, clang, ffmpeg, MySQL and lots of others): [2] [3] [4]. The tools are part of both gcc and clang compilers. We have not yet done massive testing under the Kernel AddressSanitizer (it's kind of chicken and egg problem, you need it to be upstream to start applying it extensively). To date it has found about 50 bugs. Bugs that we've found in upstream kernel are listed in [5]. We've also found ~20 bugs in out internal version of the kernel. Also people from Samsung and Oracle have found some. [...] As others noted, the main feature of AddressSanitizer is its performance due to inline compiler instrumentation and simple linear shadow memory. User-space Asan has ~2x slowdown on computational programs and ~2x memory consumption increase. Taking into account that kernel usually consumes only small fraction of CPU and memory when running real user-space programs, I would expect that kernel Asan will have ~10-30% slowdown and similar memory consumption increase (when we finish all tuning). I agree that Asan can well replace kmemcheck. We have plans to start working on Kernel MemorySanitizer that finds uses of unitialized memory. Asan+Msan will provide feature-parity with kmemcheck. As others noted, Asan will unlikely replace debug slab and pagealloc that can be enabled at runtime. Asan uses compiler instrumentation, so even if it is disabled, it still incurs visible overheads. Asan technology is easily portable to other architectures. Compiler instrumentation is fully portable. Runtime has some arch-dependent parts like shadow mapping and atomic operation interception. They are relatively easy to port." Comparison with other debugging features: ======================================== KMEMCHECK: - KASan can do almost everything that kmemcheck can. KASan uses compile-time instrumentation, which makes it significantly faster than kmemcheck. The only advantage of kmemcheck over KASan is detection of uninitialized memory reads. Some brief performance testing showed that kasan could be x500-x600 times faster than kmemcheck: $ netperf -l 30 MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET Recv Send Send Socket Socket Message Elapsed Size Size Size Time Throughput bytes bytes bytes secs. 10^6bits/sec no debug: 87380 16384 16384 30.00 41624.72 kasan inline: 87380 16384 16384 30.00 12870.54 kasan outline: 87380 16384 16384 30.00 10586.39 kmemcheck: 87380 16384 16384 30.03 20.23 - Also kmemcheck couldn't work on several CPUs. It always sets number of CPUs to 1. KASan doesn't have such limitation. DEBUG_PAGEALLOC: - KASan is slower than DEBUG_PAGEALLOC, but KASan works on sub-page granularity level, so it able to find more bugs. SLUB_DEBUG (poisoning, redzones): - SLUB_DEBUG has lower overhead than KASan. - SLUB_DEBUG in most cases are not able to detect bad reads, KASan able to detect both reads and writes. - In some cases (e.g. redzone overwritten) SLUB_DEBUG detect bugs only on allocation/freeing of object. KASan catch bugs right before it will happen, so we always know exact place of first bad read/write. [1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel [2] https://code.google.com/p/address-sanitizer/wiki/FoundBugs [3] https://code.google.com/p/thread-sanitizer/wiki/FoundBugs [4] https://code.google.com/p/memory-sanitizer/wiki/FoundBugs [5] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel#Trophies Based on work by Andrey Konovalov. Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com> Acked-by: Michal Marek <mmarek@suse.cz> Signed-off-by: Andrey Konovalov <adech.fo@gmail.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Konstantin Serebryany <kcc@google.com> Cc: Dmitry Chernenkov <dmitryc@google.com> Cc: Yuri Gribov <tetra2005@gmail.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Christoph Lameter <cl@linux.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Christoph Lameter <cl@linux.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-08Linux 3.19Linus Torvalds1-1/+1
2015-02-01Linux 3.19-rc7Linus Torvalds1-1/+1
2015-01-29ftrace: allow architectures to specify ftrace compile optionsHeiko Carstens1-1/+5
If the kernel is compiled with function tracer support the -pg compile option is passed to gcc to generate extra code into the prologue of each function. This patch replaces the "open-coded" -pg compile flag with a CC_FLAGS_FTRACE makefile variable which architectures can override if a different option should be used for code generation. Acked-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2015-01-25Linux 3.19-rc6Linus Torvalds1-1/+1
2015-01-18Linux 3.19-rc5Linus Torvalds1-1/+1
2015-01-11linux 3.19-rc4Linus Torvalds1-1/+1
2015-01-08Makefile: include arch/*/include/generated/uapi before .../generatedMichal Marek1-0/+1
The introduction of the uapi directories in v3.7-rc1 moved some of the generated headers from arch/*/include/generated to the uapi directory, keeping the #include directives intact. This creates a problem when bisecting, because the unversioned files are not cleaned automatically by git and the compiler might include stale headers as a result. Instead of cleaning them in the Makefiles, promote arch/*/include/generated/uapi in the search path. Under normal circumstances, there is no overlap between this uapi subdirectory and its parent, so the include choices remain the same. We keep arch/*/include/generated/uapi in the USERINCLUDE variable so that it is usable standalone. Note that we cannot completely swap the order of the uapi and kernel-only directories, since the headers in include/uapi/asm-generic are meant to be wrapped by their include/asm-generic counterparts when building kernel code. Reported-by: "Nicholas A. Bellinger" <nab@linux-iscsi.org> Reported-by: David Drysdale <dmd@lurklurk.org> Signed-off-by: Michal Marek <mmarek@suse.cz> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-01-08kbuild: drop $(version_h) from MRPROPER_FILESMasahiro Yamada1-1/+1
Now $(version_h) is include/generated/uapi/linux/version.h. $(version_h) in MRPROPER_FILES is redundant because it is covered by include/generated in MRPROPER_DIRS. Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com> Signed-off-by: Michal Marek <mmarek@suse.cz>
2015-01-08kbuild: use mixed-targets when two or more config targets are givenMasahiro Yamada1-1/+1
"make kvmconfig" expects that the .config has already been created, but some people might want to create the .config and run kvmconfig in one shot command, like this: $ make defconfig kvmconfig To make sure this command works correctly even if -j* option is set, we must handle them one by one. This commit turns on mixed-targets when $(MAKECMDGOALS) includes at least one config target and also includes another target. Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com> Signed-off-by: Michal Marek <mmarek@suse.cz>
2015-01-05Linux 3.19-rc3Linus Torvalds1-1/+1
2014-12-28Linux 3.19-rc2Linus Torvalds1-1/+1
2014-12-20Linux 3.19-rc1Linus Torvalds1-2/+2
2014-12-07Linux 3.18Linus Torvalds1-1/+1
2014-11-30Linux 3.18-rc7Linus Torvalds1-1/+1
2014-11-28kbuild: Fix make help-<board series> on powerpcMichal Marek1-2/+2
make ARCH=powerpc help-<board series> should not require a cofigured source tree. Also, sort the boards in the output. Signed-off-by: Michal Marek <mmarek@suse.cz>
2014-11-28kbuild: Automatically remove stale <linux/version.h> fileMichal Marek1-1/+3
In 3.7, the file moved from include/linux/ to include/generated/uapi/linux/. The path in the #include directive remained the same for compatibility reasons, but this created a problem when bisecting. Commit 9c8cdb71 (kbuild: unconditionally clobber include/linux/version.h on distclean) fixes this, provided the user does make distclean between builds. Better not rely on the user and delete the stale file each time make is invoked. Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: David Howells <dhowells@redhat.com> Signed-off-by: Michal Marek <mmarek@suse.cz>
2014-11-28Makefile: sort list of defconfig targets in make help outputKonstantin Khlebnikov1-1/+1
Without sorting this list is completely unreadable for ARCH=arm. Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@samsung.com> Signed-off-by: Michal Marek <mmarek@suse.cz>
2014-11-26kbuild: collect shorthands into scripts/Kbuild.includeMasahiro Yamada1-7/+0
The shorthand "clean" is defined in both the top Makefile and scripts/Makefile.clean. Likewise, the "hdr-inst" is defined in both the top Makefile and scripts/Makefile.headersinst. To reduce code duplication, this commit collects them into scripts/Kbuild.include like the "build" and "modbuiltin" shorthands. It requires scripts/Makefile.clean to include scripts/Kbuild.include, but its impact on the performance of "make clean" should be negligible. Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com> Signed-off-by: Michal Marek <mmarek@suse.cz>
2014-11-23Linux 3.18-rc6Linus Torvalds1-1/+1
2014-11-16Linux 3.18-rc5Linus Torvalds1-1/+1
2014-11-15kernel: use the gnu89 standard explicitlyKirill A. Shutemov1-2/+3
Sasha Levin reports: "gcc5 changes the default standard to c11, which makes kernel build unhappy Explicitly define the kernel standard to be gnu89 which should keep everything working exactly like it was before gcc5" There are multiple small issues with the new default, but the biggest issue seems to be that the old - and very useful - GNU extension to allow a cast in front of an initializer has gone away. Patch updated by Kirill: "I'm pretty sure all gcc versions you can build kernel with supports -std=gnu89. cc-option is redunrant. We also need to adjust HOSTCFLAGS otherwise allmodconfig fails for me" Note by Andrew Pinski: "Yes it was reported and both problems relating to this extension has been added to gnu99 and gnu11. Though there are other issues with the kernel dealing with extern inline have different semantics between gnu89 and gnu99/11" End result: we may be able to move up to a newer stdc model eventually, but right now the newer models have some annoying deficiencies, so the traditional "gnu89" model ends up being the preferred one. Signed-off-by: Sasha Levin <sasha.levin@oracle.com> Singed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-11-09Linux 3.18-rc4Linus Torvalds1-1/+1
2014-11-02Linux 3.18-rc3Linus Torvalds1-2/+2
2014-10-26Linux 3.18-rc2Linus Torvalds1-1/+1
2014-10-19Linux 3.18-rc1Linus Torvalds1-2/+2
2014-10-05Linux 3.17Linus Torvalds1-1/+1
2014-10-02kbuild: Do not reference *-n variables in the MakefileMichal Marek1-3/+1
Kconfig options are either 'y', 'm', or undefined. Signed-off-by: Michal Marek <mmarek@suse.cz>
2014-10-02kbuild: simplify build, clean, modbuiltin shorthandsMasahiro Yamada1-1/+1
$(if $(KBUILD_SRC),$(srctree)/) was a useful strategy to omit a long absolute path for in-source-tree build prior to commit 890676c65d699db3ad82e7dddd0cf8fb449031af (kbuild: Use relative path when building in the source tree). Now $(srctree) is "." when building in the source tree. It would not be annoying to add "$(srctree)/" all the time. Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com> Signed-off-by: Michal Marek <mmarek@suse.cz>
2014-10-01kbuild: handle C=... and M=... after entering into build directoryMasahiro Yamada1-31/+29
This commit avoids processing C=... and M=... twice when O=... is also given. Besides, we can also remove KBUILD_EXTMOD="$(KBUILD_EXTMOD)" in the sub-make target. Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com> Acked-by: Peter Foley <pefoley2@pefoley.com> Signed-off-by: Michal Marek <mmarek@suse.cz>
2014-10-01kbuild: use $(Q) for sub-make targetMasahiro Yamada1-2/+1
Since commit 066b7ed9558087a7957a1128f27d7a3462ff117f (kbuild: Do not print the build directory with make -s), "Q" is defined above the sub-make target. This commit takes advantage of that and replaces "$(if $(KBUILD_VERBOSE:1=),@)" with "$(Q)". Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com> Acked-by: Peter Foley <pefoley2@pefoley.com> Signed-off-by: Michal Marek <mmarek@suse.cz>
2014-10-01kbuild: fake the "Entering directory ..." message more simplyMasahiro Yamada1-11/+8
Commit c2e28dc975ea87feed84415006ae143424912ac7 (kbuild: Print the name of the build directory) added a gimmick to show the "Entering directory ...". Instead of echoing the hard-coded message (that is, we need to know the exact message), moving --no-print-directory would be easier. Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com> Acked-by: Peter Foley <pefoley2@pefoley.com> Signed-off-by: Michal Marek <mmarek@suse.cz>
2014-09-28Linux 3.17-rc7Linus Torvalds1-1/+1
2014-09-26Make Documenation depend on headers_installPeter Foley1-0/+2
Cc: rdunlap@infradead.org Cc: linux-doc@vger.kernel.org Cc: sudeep.dutt@intel.com Cc: nikhil.rao@intel.com Cc: ashutosh.dixit@intel.com Cc: akpm@linux-foundation.org Cc: gregkh@linuxfoundation.org Signed-off-by: Peter Foley <pefoley2@pefoley.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2014-09-21Linux 3.17-rc6Linus Torvalds1-1/+1
2014-09-14Linux 3.17-rc5Linus Torvalds1-1/+1
2014-09-07Linux 3.17-rc4Linus Torvalds1-1/+1
2014-08-31Linux 3.17-rc3Linus Torvalds1-1/+1
2014-08-27kbuild: handle module compression while running 'make modules_install'.Bertrand Jacquin1-0/+15
Since module-init-tools (gzip) and kmod (gzip and xz) support compressed modules, it could be useful to include a support for compressing modules right after having them installed. Doing this in kbuild instead of per distro can permit to make this kind of usage more generic. This patch add a Kconfig entry to "Enable loadable module support" menu and let you choose to compress using gzip (default) or xz. Both gzip and xz does not used any extra -[1-9] option since Andi Kleen and Rusty Russell prove no gain is made using them. gzip is called with -n argument to avoid storing original filename inside compressed file, that way we can save some more bytes. On a v3.16 kernel, 'make allmodconfig' generated 4680 modules for a total of 378MB (no strip, no sign, no compress), the following table shows observed disk space gain based on the allmodconfig .config : | time | +-------------+-----------------+ | manual .ko | make | size | percent | compression | modules_install | | gain +-------------+-----------------+------+-------- - | | 18.61s | 378M | GZIP | 3m16s | 3m37s | 102M | 73.41% XZ | 5m22s | 5m39s | 77M | 79.83% The gain for restricted environnement seems to be interesting while uncompress can be time consuming but happens only while loading a module, that is generally done only once. This is fully compatible with signed modules while the signed module is compressed. module-init-tools or kmod handles decompression and provide to other layer the uncompressed but signed payload. Reviewed-by: Willy Tarreau <w@1wt.eu> Signed-off-by: Bertrand Jacquin <beber@meleeweb.net> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2014-08-25Linux 3.17-rc2Linus Torvalds1-1/+1
2014-08-16Linux 3.17-rc1Linus Torvalds1-2/+2
2014-08-07kbuild: kselftest - new make target to build and run kernel selftestsShuah Khan1-0/+12
Add a new make target "kselftest" to enable kernel testing. This new target builds and runs kernel selftests. Running as root is recommended for a complete test run as some tests don't run when run by non-root user. Build, install, and boot kernel before running kselftest on it. Signed-off-by: Shuah Khan <shuah.kh@samsung.com> Acked-by: Sam Ravnborg <sam@ravnborg.org> Signed-off-by: Michal Marek <mmarek@suse.cz>
2014-08-06./Makefile: tell gcc optimizer to never introduce new data racesJiri Kosina1-0/+3
We have been chasing a memory corruption bug, which turned out to be caused by very old gcc (4.3.4), which happily turned conditional load into a non-conditional one, and that broke correctness (the condition was met only if lock was held) and corrupted memory. This particular problem with that particular code did not happen when never gccs were used. I've brought this up with our gcc folks, as I wanted to make sure that this can't really happen again, and it turns out it actually can. Quoting Martin Jambor <mjambor@suse.cz>: "More current GCCs are more careful when it comes to replacing a conditional load with a non-conditional one, most notably they check that a store happens in each iteration of _a_ loop but they assume loops are executed. They also perform a simple check whether the store cannot trap which currently passes only for non-const variables. A simple testcase demonstrating it on an x86_64 is for example the following: $ cat cond_store.c int g_1 = 1; int g_2[1024] __attribute__((section ("safe_section"), aligned (4096))); int c = 4; int __attribute__ ((noinline)) foo (void) { int l; for (l = 0; (l != 4); l++) { if (g_1) return l; for (g_2[0] = 0; (g_2[0] >= 26); ++g_2[0]) ; } return 2; } int main (int argc, char* argv[]) { if (mprotect (g_2, sizeof(g_2), PROT_READ) == -1) { int e = errno; error (e, e, "mprotect error %i", e); } foo (); __builtin_printf("OK\n"); return 0; } /* EOF */ $ ~/gcc/trunk/inst/bin/gcc cond_store.c -O2 --param allow-store-data-races=0 $ ./a.out OK $ ~/gcc/trunk/inst/bin/gcc cond_store.c -O2 --param allow-store-data-races=1 $ ./a.out Segmentation fault The testcase fails the same at least with 4.9, 4.8 and 4.7. Therefore I would suggest building kernels with this parameter set to zero. I also agree with Jikos that the default should be changed for -O2. I have run most of the SPEC 2k6 CPU benchmarks (gamess and dealII failed, at -O2, not sure why) compiled with and without this option and did not see any real difference between respective run-times" Hopefully the default will be changed in newer gccs, but let's force it for kernel builds so that we are on a safe side even when older gcc are used. The code in question was out-of-tree printk-in-NMI (yeah, surprise suprise, once again) patch written by Petr Mladek, let me quote his comment from our internal bugzilla: "I have spent few days investigating inconsistent state of kernel ring buffer. It went out that it was caused by speculative store generated by gcc-4.3.4. The problem is in assembly generated for make_free_space(). The functions is called the following way: + vprintk_emit(); + log = MAIN_LOG; // with logbuf_lock or log = NMI_LOG; // with nmi_logbuf_lock cont_add(log, ...); + cont_flush(log, ...); + log_store(log, ...); + log_make_free_space(log, ...); If called with log = NMI_LOG then only nmi_log_* global variables are safe to modify but the generated code does store also into (main_)log_* global variables: <log_make_free_space>: 55 push %rbp 89 f6 mov %esi,%esi 48 8b 05 03 99 51 01 mov 0x1519903(%rip),%rax # ffffffff82620868 <nmi_log_next_id> 44 8b 1d ec 98 51 01 mov 0x15198ec(%rip),%r11d # ffffffff82620858 <log_next_idx> 8b 35 36 60 14 01 mov 0x1146036(%rip),%esi # ffffffff8224cfa8 <log_buf_len> 44 8b 35 33 60 14 01 mov 0x1146033(%rip),%r14d # ffffffff8224cfac <nmi_log_buf_len> 4c 8b 2d d0 98 51 01 mov 0x15198d0(%rip),%r13 # ffffffff82620850 <log_next_seq> 4c 8b 25 11 61 14 01 mov 0x1146111(%rip),%r12 # ffffffff8224d098 <log_buf> 49 89 c2 mov %rax,%r10 48 21 c2 and %rax,%rdx 48 8b 1d 0c 99 55 01 mov 0x155990c(%rip),%rbx # ffffffff826608a0 <nmi_log_buf> 49 c1 ea 20 shr $0x20,%r10 48 89 55 d0 mov %rdx,-0x30(%rbp) 44 29 de sub %r11d,%esi 45 29 d6 sub %r10d,%r14d 4c 8b 0d 97 98 51 01 mov 0x1519897(%rip),%r9 # ffffffff82620840 <log_first_seq> eb 7e jmp ffffffff81107029 <log_make_free_space+0xe9> [...] 85 ff test %edi,%edi # edi = 1 for NMI_LOG 4c 89 e8 mov %r13,%rax 4c 89 ca mov %r9,%rdx 74 0a je ffffffff8110703d <log_make_free_space+0xfd> 8b 15 27 98 51 01 mov 0x1519827(%rip),%edx # ffffffff82620860 <nmi_log_first_id> 48 8b 45 d0 mov -0x30(%rbp),%rax 48 39 c2 cmp %rax,%rdx # end of loop 0f 84 da 00 00 00 je ffffffff81107120 <log_make_free_space+0x1e0> [...] 85 ff test %edi,%edi # edi = 1 for NMI_LOG 4c 89 0d 17 97 51 01 mov %r9,0x1519717(%rip) # ffffffff82620840 <log_first_seq> ^^^^^^^^^^^^^^^^^^^^^^^^^^ KABOOOM 74 35 je ffffffff81107160 <log_make_free_space+0x220> It stores log_first_seq when edi == NMI_LOG. This instructions are used also when edi == MAIN_LOG but the store is done speculatively before the condition is decided. It is unsafe because we do not have "logbuf_lock" in NMI context and some other process migh modify "log_first_seq" in parallel" I believe that the best course of action is both - building kernel (and anything multi-threaded, I guess) with that optimization turned off - persuade gcc folks to change the default for future releases Signed-off-by: Jiri Kosina <jkosina@suse.cz> Cc: Martin Jambor <mjambor@suse.cz> Cc: Petr Mladek <pmladek@suse.cz> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Marek Polacek <polacek@redhat.com> Cc: Jakub Jelinek <jakub@redhat.com> Cc: Steven Noonan <steven@uplinklabs.net> Cc: Richard Biener <richard.guenther@gmail.com> Cc: Dan Carpenter <dan.carpenter@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>