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Right now, TINY_RCU depends on (!PREEMPTION && !SMP), which has served the
kernel well for many years due to the fact that PREEMPT_RCU is normally
a synonym for PREEMPTION. But with the advent of lazy preemption,
it will be possible to have non-preemptible RCU in a preemptible kernel,
so that kernels could be built with PREEMPT_RCU=n and PREEMPTION=y.
This commit therefore makes TINY_RCU depend on (!PREEMPT_RCU && !SMP),
thus allowing for a non-preemptible RCU in preemptible kernels.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Ankur Arora <ankur.a.arora@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
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With Ankur's lazy-/auto-preemption patches applied and with a
lazy-preemptible kernel in combination with a non-preemptible RCU,
lockdep sometimes complains about context switches within RCU read-side
critical sections. This is a false positive due to rcu_read_unlock()
updating lockdep state too late:
__release(RCU);
__rcu_read_unlock();
// Context switch here results in lockdep false positive!!!
rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
Although this complaint could also happen with preemptible RCU
in a preemptible kernel, the odds of that happening aer quite low.
In constrast, with non-preemptible RCU, a long critical section has a
high probability of performing a context switch from the preempt_enable()
in __rcu_read_unlock().
The fix is straightforward, just move the rcu_lock_release()
within rcu_read_unlock() to obtain the reverse order from that of
rcu_read_lock():
rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
__release(RCU);
__rcu_read_unlock();
This commit makes this change.
Co-developed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Co-developed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Ankur Arora <ankur.a.arora@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
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There is some indications that rcu_softirq_qs() might be more generally
used than anticipated. This commit therefore adds some lockdep assertions
and some cautionary tales in a new kernel-doc header.
Link: https://lore.kernel.org/all/Zd4DXTyCf17lcTfq@debian.debian/
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Yan Zhai <yan@cloudflare.com>
Cc: <netdev@vger.kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
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Fixed a typo in some variables where height was misspelled as heigth.
Signed-off-by: Isak Ellmer <isak01@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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As of the first s390 pull request during the 6.9 merge window,
commit 691632f0e869 ("Merge tag 's390-6.9-1' of
git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux"), s390 can be
built with LLVM=1 when using LLVM 18.1.0, which is the first version
that has SystemZ support implemented in ld.lld and llvm-objcopy.
Update the supported architectures table in the Kbuild LLVM
documentation to note this explicitly to make it more discoverable by
users and other developers. Additionally, this brings s390 in line with
the rest of the architectures in the table, which all support LLVM=1.
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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When KCSAN and CONSTRUCTORS are enabled, one can trigger the
"Unpatched return thunk in use. This should not happen!"
catch-all warning.
Usually, when objtool runs on the .o objects, it does generate a section
.return_sites which contains all offsets in the objects to the return
thunks of the functions present there. Those return thunks then get
patched at runtime by the alternatives.
KCSAN and CONSTRUCTORS add this to the object file's .text.startup
section:
-------------------
Disassembly of section .text.startup:
...
0000000000000010 <_sub_I_00099_0>:
10: f3 0f 1e fa endbr64
14: e8 00 00 00 00 call 19 <_sub_I_00099_0+0x9>
15: R_X86_64_PLT32 __tsan_init-0x4
19: e9 00 00 00 00 jmp 1e <__UNIQUE_ID___addressable_cryptd_alloc_aead349+0x6>
1a: R_X86_64_PLT32 __x86_return_thunk-0x4
-------------------
which, if it is built as a module goes through the intermediary stage of
creating a <module>.mod.c file which, when translated, receives a second
constructor:
-------------------
Disassembly of section .text.startup:
0000000000000010 <_sub_I_00099_0>:
10: f3 0f 1e fa endbr64
14: e8 00 00 00 00 call 19 <_sub_I_00099_0+0x9>
15: R_X86_64_PLT32 __tsan_init-0x4
19: e9 00 00 00 00 jmp 1e <_sub_I_00099_0+0xe>
1a: R_X86_64_PLT32 __x86_return_thunk-0x4
...
0000000000000030 <_sub_I_00099_0>:
30: f3 0f 1e fa endbr64
34: e8 00 00 00 00 call 39 <_sub_I_00099_0+0x9>
35: R_X86_64_PLT32 __tsan_init-0x4
39: e9 00 00 00 00 jmp 3e <__ksymtab_cryptd_alloc_ahash+0x2>
3a: R_X86_64_PLT32 __x86_return_thunk-0x4
-------------------
in the .ko file.
Objtool has run already so that second constructor's return thunk cannot
be added to the .return_sites section and thus the return thunk remains
unpatched and the warning rightfully fires.
Drop KCSAN flags from the mod.c generation stage as those constructors
do not contain data races one would be interested about.
Debugged together with David Kaplan <David.Kaplan@amd.com> and Nikolay
Borisov <nik.borisov@suse.com>.
Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
Closes: https://lore.kernel.org/r/0851a207-7143-417e-be31-8bf2b3afb57d@molgen.mpg.de
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Paul Menzel <pmenzel@molgen.mpg.de> # Dell XPS 13
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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The -Woverride-init warn about code that may be intentional or not,
but the inintentional ones tend to be real bugs, so there is a bit of
disagreement on whether this warning option should be enabled by default
and we have multiple settings in scripts/Makefile.extrawarn as well as
individual subsystems.
Older versions of clang only supported -Wno-initializer-overrides with
the same meaning as gcc's -Woverride-init, though all supported versions
now work with both. Because of this difference, an earlier cleanup of
mine accidentally turned the clang warning off for W=1 builds and only
left it on for W=2, while it's still enabled for gcc with W=1.
There is also one driver that only turns the warning off for newer
versions of gcc but not other compilers, and some but not all the
Makefiles still use a cc-disable-warning conditional that is no
longer needed with supported compilers here.
Address all of the above by removing the special cases for clang
and always turning the warning off unconditionally where it got
in the way, using the syntax that is supported by both compilers.
Fixes: 2cd3271b7a31 ("kbuild: avoid duplicate warning options")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Andrew Jeffery <andrew@codeconstruct.com.au>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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When compiling the v6.9-rc1 kernel with the x32 compiler, the following
errors are reported. The reason is that we take an "unsigned long"
variable and print it using "PRIx64" format string.
In file included from check.c:16:
check.c: In function ‘add_dead_ends’:
/usr/src/git/linux-2.6/tools/objtool/include/objtool/warn.h:46:17: error: format ‘%llx’ expects argument of type ‘long long unsigned int’, but argument 5 has type ‘long unsigned int’ [-Werror=format=]
46 | "%s: warning: objtool: " format "\n", \
| ^~~~~~~~~~~~~~~~~~~~~~~~
check.c:613:33: note: in expansion of macro ‘WARN’
613 | WARN("can't find unreachable insn at %s+0x%" PRIx64,
| ^~~~
...
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: linux-kernel@vger.kernel.org
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Commit c33621b4c5ad ("x86/virt/tdx: Wire up basic SEAMCALL functions")
introduced a new instance of core-y instead of the standardized obj-y
syntax.
X86 Makefiles descend into subdirectories of arch/x86/virt inconsistently;
into arch/x86/virt/ via core-y defined in arch/x86/Makefile, but into
arch/x86/virt/svm/ via obj-y defined in arch/x86/Kbuild.
This is problematic when you build a single object in parallel because
multiple threads attempt to build the same file.
$ make -j$(nproc) arch/x86/virt/vmx/tdx/seamcall.o
[ snip ]
AS arch/x86/virt/vmx/tdx/seamcall.o
AS arch/x86/virt/vmx/tdx/seamcall.o
fixdep: error opening file: arch/x86/virt/vmx/tdx/.seamcall.o.d: No such file or directory
make[4]: *** [scripts/Makefile.build:362: arch/x86/virt/vmx/tdx/seamcall.o] Error 2
Use the obj-y syntax, as it works correctly.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240330060554.18524-1-masahiroy@kernel.org
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Paul E. McKenney
Uladzislau Rezki (Sony)
Linus Torvalds
Isak Ellmer
Nathan Chancellor
Borislav Petkov (AMD)
Arnd Bergmann
Mikulas Patocka
Masahiro Yamada