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module: Use RCU instead of RCU-sched.#50

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module: Use RCU instead of RCU-sched.#50
modules-kpd-app[bot] wants to merge 28 commits intomodules-next_basefrom
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Pull request for series with
subject: module: Use RCU instead of RCU-sched.
version: 3
url: https://patchwork.kernel.org/project/linux-modules/list/?series=923281

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modules-kpd-app bot commented Jan 15, 2025

Upstream branch: 0217859
series: https://patchwork.kernel.org/project/linux-modules/list/?series=923281
version: 3

Sebastian Andrzej Siewior added 24 commits January 28, 2025 08:22
@mcgrof
module: Begin to move from RCU-sched to RCU.
85546b0 
The RCU usage in module was introduced in commit d72b375 ("Remove
stop_machine during module load v2") and it claimed not to be RCU but
similar. Then there was another improvement in commit e91defa
("module: don't use stop_machine on module load"). It become a mix of
RCU and RCU-sched and was eventually fixed 0be964b ("module:
Sanitize RCU usage and locking"). Later RCU & RCU-sched was merged in
commit cb2f553 ("modules: Replace synchronize_sched() and
call_rcu_sched()") so that was aligned.

Looking at it today, there is still leftovers. The preempt_disable() was
used instead rcu_read_lock_sched(). The RCU & RCU-sched merge was not
complete as there is still rcu_dereference_sched() for module::kallsyms.

The RCU-list modules and unloaded_tainted_modules are always accessed
under RCU protection or the module_mutex. The modules list iteration can
always happen safely because the module will not disappear.
Once the module is removed (free_module()) then after removing the
module from the list, there is a synchronize_rcu() which waits until
every RCU reader left the section. That means iterating over the list
within a RCU-read section is enough, there is no need to disable
preemption. module::kallsyms is first assigned in add_kallsyms() before
the module is added to the list. At this point, it points to init data.
This pointer is later updated and before the init code is removed there
is also synchronize_rcu() in do_free_init(). That means A RCU read lock
is enough for protection and rcu_dereference() can be safely used.

Convert module code and its users step by step. Update comments and
convert print_modules() to use RCU.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
module: Use proper RCU assignment in add_kallsyms().
fa89193 
add_kallsyms() assigns the RCU pointer module::kallsyms and setups the
structures behind it which point to init-data. The module was not
published yet, nothing can see the kallsyms pointer and the data behind
it. Also module's init function was not yet invoked.
There is no need to use rcu_dereference() here, it is just to keep
checkers quiet. The whole RCU read section is also not needed.

Use a local kallsyms pointer and setup the data structures. Assign that
pointer to the data structure at the end via rcu_assign_pointer().

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
module: Use RCU in find_kallsyms_symbol().
fc48e7d 
The modules list and module::kallsyms can be accessed under RCU
assumption.

Use rcu_dereference() to reference the kallsyms pointer in
find_kallsyms_symbol().  Use a RCU section instead of preempt_disable in
callers of find_kallsyms_symbol(). Keep the preempt-disable in
module_address_lookup() due to __module_address().

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
module: Use RCU in module_get_kallsym().
fa493cb 
The modules list and module::kallsyms can be accessed under RCU
assumption.

Iterate the modules with RCU protection, use rcu_dereference() to access
the kallsyms pointer.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
module: Use RCU in find_module_all().
862a4e9 
The modules list and module::kallsyms can be accessed under RCU
assumption.

Remove module_assert_mutex_or_preempt() from find_module_all() so it can
be used under RCU protection without warnings. Update its callers to use
RCU protection instead of preempt_disable().

Cc: Jiri Kosina <jikos@kernel.org>
Cc: Joe Lawrence <joe.lawrence@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-trace-kernel@vger.kernel.org
Cc: live-patching@vger.kernel.org
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
module: Use RCU in __find_kallsyms_symbol_value().
da8322c 
module::kallsyms can be accessed under RCU assumption.

Use rcu_dereference() to access module::kallsyms.
Update callers.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
module: Use RCU in module_kallsyms_on_each_symbol().
b8e1fff 
module::kallsyms can be accessed under RCU assumption.

Use rcu_dereference() to access module::kallsyms.
Update callers.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
module: Remove module_assert_mutex_or_preempt() from try_add_tainted_…
d4096c9 
…module().

module_assert_mutex_or_preempt() is not needed in
try_add_tainted_module(). The function checks for RCU-sched or the
module_mutex to be acquired. The list_for_each_entry_rcu() below does
the same check.

Remove module_assert_mutex_or_preempt() from try_add_tainted_module().

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
module: Use RCU in find_symbol().
1ab78a9 
module_assert_mutex_or_preempt() is not needed in find_symbol(). The
function checks for RCU-sched or the module_mutex to be acquired. The
list_for_each_entry_rcu() below does the same check.

Remove module_assert_mutex_or_preempt() from try_add_tainted_module().
Use RCU protection to invoke find_symbol() and update callers.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
module: Use RCU in __is_module_percpu_address().
2797927 
The modules list can be accessed under RCU assumption.

Use RCU protection instead preempt_disable().

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
module: Allow __module_address() to be called from RCU section.
a44cfd0 
mod_find() uses either the modules list to find a module or a tree
lookup (CONFIG_MODULES_TREE_LOOKUP). The list and the tree can both be
iterated under RCU assumption (as well as RCU-sched).

Remove module_assert_mutex_or_preempt() from __module_address() and
entirely since __module_address() is the last user.
Update comments.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
module: Use RCU in search_module_extables().
5387c73 
search_module_extables() returns an exception_table_entry belonging to a
module. The lookup via __module_address() can be performed with RCU
protection.
The returned exception_table_entry remains valid because the passed
address usually belongs to a module that is currently executed. So the
module can not be removed because "something else" holds a reference to
it, ensuring that it can not be removed.
Exceptions here are:
- kprobe, acquires a reference on the module beforehand
- MCE, invokes the function from within a timer and the RCU lifetime
  guarantees (of the timer) are sufficient.

Therefore it is safe to return the exception_table_entry outside the RCU
section which provided the module.

Use RCU for the lookup in search_module_extables() and update the
comment.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
module: Use RCU in all users of __module_address().
bbb5c14 
__module_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_address() with
RCU.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
module: Use RCU in all users of __module_text_address().
4ff935a 
__module_text_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_text_address()
with RCU.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
ARM: module: Use RCU in all users of __module_text_address().
0c1e43a 
__module_text_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_text_address()
with RCU.

Cc: Russell King <linux@armlinux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
arm64: module: Use RCU in all users of __module_text_address().
710213b 
__module_text_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_text_address()
with RCU.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-trace-kernel@vger.kernel.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
LoongArch/orc: Use RCU in all users of __module_address().
f016e40 
__module_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_address() with
RCU.

Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: loongarch@lists.linux.dev
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
LoongArch: ftrace: Use RCU in all users of __module_text_address().
91fc8e2 
__module_text_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_text_address()
with RCU.

Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: linux-trace-kernel@vger.kernel.org
Cc: loongarch@lists.linux.dev
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
powerpc/ftrace: Use RCU in all users of __module_text_address().
8ad1cb4 
__module_text_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_text_address()
with RCU.

Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Naveen N Rao <naveen@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-trace-kernel@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
@mcgrof
cfi: Use RCU while invoking __module_address().
810c627 
__module_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

The _notrace() variant was introduced in commit 14c4c8e ("cfi: Use
rcu_read_{un}lock_sched_notrace"). The recursive case where
__cfi_slowpath_diag() could end up calling itself is no longer present,
as all that logic is gone since commit 8924560 ("cfi: Switch to
-fsanitize=kcfi").
Sami Tolvanen said that KCFI checks don't perform function calls.

Elliot Berman verified it with
| modprobe -a dummy_stm stm_ftrace stm_p_basic
| mkdir -p /sys/kernel/config/stp-policy/dummy_stm.0.my-policy/default
| echo function > /sys/kernel/tracing/current_tracer
| echo 1 > /sys/kernel/tracing/tracing_on
| echo dummy_stm.0 > /sys/class/stm_source/ftrace/stm_source_link

Replace the rcu_read_lock_sched_notrace() section around
__module_address() with RCU.

Cc: Elliot Berman <quic_eberman@quicinc.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: llvm@lists.linux.dev
Tested-by: Elliot Berman <elliot.berman@oss.qualcomm.com>  # sm8650-qrd
Link: https://lore.kernel.org/all/20241230185812429-0800.eberman@hu-eberman-lv.qualcomm.com
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
x86: Use RCU in all users of __module_address().
e19dcdd 
__module_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_address() with
RCU.

Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
jump_label: Use RCU in all users of __module_address().
15084c2 
__module_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_address() with RCU.

Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
jump_label: Use RCU in all users of __module_text_address().
24762a3 
__module_text_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_text_address()
with RCU.

Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
bpf: Use RCU in all users of __module_text_address().
9bce666 
__module_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_address() with
RCU.

Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Hao Luo <haoluo@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Matt Bobrowski <mattbobrowski@google.com>
Cc: Song Liu <song@kernel.org>
Cc: Stanislav Fomichev <sdf@fomichev.me>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: bpf@vger.kernel.org
Cc: linux-trace-kernel@vger.kernel.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Sebastian Andrzej Siewior added 3 commits January 28, 2025 08:22
@mcgrof
kprobes: Use RCU in all users of __module_text_address().
b93277f 
__module_text_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_text_address()
with RCU.

Cc: David S. Miller <davem@davemloft.net>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Naveen N Rao <naveen@kernel.org>
Cc: linux-trace-kernel@vger.kernel.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
static_call: Use RCU in all users of __module_text_address().
c1c3fca 
__module_text_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_text_address()
with RCU.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
@mcgrof
bug: Use RCU instead RCU-sched to protect module_bug_list.
b70703b 
The list module_bug_list relies on module_mutex for writer
synchronisation. The list is already RCU style.
The list removal is synchronized with modules' synchronize_rcu() in
free_module().

Use RCU read lock protection instead of RCU-sched.

Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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modules-kpd-app bot commented Jan 28, 2025

Upstream branch: f3b9354
series: https://patchwork.kernel.org/project/linux-modules/list/?series=923281
version: 3

@modules-kpd-app modules-kpd-app bot force-pushed the series/919984=>modules-next branch from e247328 to b70703b Compare January 28, 2025 08:22
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modules-kpd-app bot commented Jan 30, 2025

At least one diff in series https://patchwork.kernel.org/project/linux-modules/list/?series=923281 irrelevant now. Closing PR.

@modules-kpd-app modules-kpd-app bot added accepted and removed new labels Jan 30, 2025
@modules-kpd-app modules-kpd-app bot closed this Jan 30, 2025
@modules-kpd-app modules-kpd-app bot deleted the series/919984=>modules-next branch January 30, 2025 14:42
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