6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Qi Xi xiqi2@huawei.com
[ Upstream commit edcc8a38b5ac1a3dbd05e113a38a25b937ebefe5 ]
The commit c2c60ea37e5b ("once: use __section(".data.once")") moved DO_ONCE's ___done variable to .data.once section, which conflicts with DO_ONCE_LITE() that also uses the same section.
This creates a race condition when clear_warn_once is used:
Thread 1 (DO_ONCE) Thread 2 (DO_ONCE) __do_once_start read ___done (false) acquire once_lock execute func __do_once_done write ___done (true) __do_once_start release once_lock // Thread 3 clear_warn_once reset ___done read ___done (false) acquire once_lock execute func schedule once_work __do_once_done once_deferred: OK write ___done (true) static_branch_disable release once_lock schedule once_work once_deferred: BUG_ON(!static_key_enabled)
DO_ONCE_LITE() in once_lite.h is used by WARN_ON_ONCE() and other warning macros. Keep its ___done flag in the .data..once section and allow resetting by clear_warn_once, as originally intended.
In contrast, DO_ONCE() is used for functions like get_random_once() and relies on its ___done flag for internal synchronization. We should not reset DO_ONCE() by clear_warn_once.
Fix it by isolating DO_ONCE's ___done into a separate .data..do_once section, shielding it from clear_warn_once.
Fixes: c2c60ea37e5b ("once: use __section(".data.once")") Reported-by: Hulk Robot hulkci@huawei.com Signed-off-by: Qi Xi xiqi2@huawei.com Signed-off-by: Arnd Bergmann arnd@arndb.de Signed-off-by: Sasha Levin sashal@kernel.org --- include/asm-generic/vmlinux.lds.h | 1 + include/linux/once.h | 4 ++-- 2 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index cf3f8b9bf43f0..010ac18c05916 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -351,6 +351,7 @@ __start_once = .; \ *(.data..once) \ __end_once = .; \ + *(.data..do_once) \ STRUCT_ALIGN(); \ *(__tracepoints) \ /* implement dynamic printk debug */ \ diff --git a/include/linux/once.h b/include/linux/once.h index 30346fcdc7995..449a0e34ad5ad 100644 --- a/include/linux/once.h +++ b/include/linux/once.h @@ -46,7 +46,7 @@ void __do_once_sleepable_done(bool *done, struct static_key_true *once_key, #define DO_ONCE(func, ...) \ ({ \ bool ___ret = false; \ - static bool __section(".data..once") ___done = false; \ + static bool __section(".data..do_once") ___done = false; \ static DEFINE_STATIC_KEY_TRUE(___once_key); \ if (static_branch_unlikely(&___once_key)) { \ unsigned long ___flags; \ @@ -64,7 +64,7 @@ void __do_once_sleepable_done(bool *done, struct static_key_true *once_key, #define DO_ONCE_SLEEPABLE(func, ...) \ ({ \ bool ___ret = false; \ - static bool __section(".data..once") ___done = false; \ + static bool __section(".data..do_once") ___done = false; \ static DEFINE_STATIC_KEY_TRUE(___once_key); \ if (static_branch_unlikely(&___once_key)) { \ ___ret = __do_once_sleepable_start(&___done); \