kernel/linux.git/include/linux/once_lite.h, branch v6.19.11

include/linux/once_lite.h: fix judgment in WARN_ONCE with clang

2025-11-20T22:03:43+00:00

For c code: ```c extern int xx; void test(void) { if (WARN_ONCE(xx, "x")) __asm__ volatile ("nop":::); } ``` Clang will generate the following assembly code: ```assemble test: movl xx(%rip), %eax // Assume xx == 0 (likely case) testl %eax, %eax // judge once je .LBB0_3 // jump to .LBB0_3 testb $1, test.__already_done(%rip) je .LBB0_2 .LBB0_3: testl %eax, %eax // judge again je .LBB0_5 // jump to .LBB0_5 .LBB0_4: nop .LBB0_5: retq // omit ``` In the above code, `xx == 0` should be a likely case, but in this case, xx has been judged twice. Test info: 1. kernel source: linux-next commit 9c0826a5d9aa4d52206d ("Add linux-next specific files for 20251107") 2. compiler: clang: Debian clang version 21.1.4 (8) with Debian LLD 21.1.4 (compatible with GNU linkers) 3. config: base on default x86_64_defconfig, and setting: CONFIG_MITIGATION_RETHUNK=n CONFIG_STACKPROTECTOR=n Add unlikely to __ret_cond to help the compiler optimize correctly. [akpm@linux-foundation.org: undo whitespace changes] Link: https://lkml.kernel.org/r/20251109083715.24495-1-qq570070308@gmail.com Signed-off-by: Xie Yuanbin Cc: Bill Wendling Cc: Jan Kara Cc: Justin Stitt Cc: Maninder Singh Cc: Masahiro Yamada Cc: Nathan Chancellor Cc: Will Deacon Signed-off-by: Andrew Morton

Rename .data.once to .data..once to fix resetting WARN*_ONCE

2024-11-27T00:38:27+00:00

Commit b1fca27d384e ("kernel debug: support resetting WARN*_ONCE") added support for clearing the state of once warnings. However, it is not functional when CONFIG_LD_DEAD_CODE_DATA_ELIMINATION or CONFIG_LTO_CLANG is enabled, because .data.once matches the .data.[0-9a-zA-Z_]* pattern in the DATA_MAIN macro. Commit cb87481ee89d ("kbuild: linker script do not match C names unless LD_DEAD_CODE_DATA_ELIMINATION is configured") was introduced to suppress the issue for the default CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=n case, providing a minimal fix for stable backporting. We were aware this did not address the issue for CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y. The plan was to apply correct fixes and then revert cb87481ee89d. [1] Seven years have passed since then, yet the #ifdef workaround remains in place. Meanwhile, commit b1fca27d384e introduced the .data.once section, and commit dc5723b02e52 ("kbuild: add support for Clang LTO") extended the #ifdef. Using a ".." separator in the section name fixes the issue for CONFIG_LD_DEAD_CODE_DATA_ELIMINATION and CONFIG_LTO_CLANG. [1]: https://lore.kernel.org/linux-kbuild/CAK7LNASck6BfdLnESxXUeECYL26yUDm0cwRZuM4gmaWUkxjL5g@mail.gmail.com/ Fixes: b1fca27d384e ("kernel debug: support resetting WARN*_ONCE") Fixes: dc5723b02e52 ("kbuild: add support for Clang LTO") Signed-off-by: Masahiro Yamada

x86/extable: Fix ex_handler_msr() print condition

2022-07-21T08:39:42+00:00

On Fri, Jun 17, 2022 at 02:08:52PM +0300, Stephane Eranian wrote: > Some changes to the way invalid MSR accesses are reported by the > kernel is causing some problems with messages printed on the > console. > > We have seen several cases of ex_handler_msr() printing invalid MSR > accesses once but the callstack multiple times causing confusion on > the console. > The problem here is that another earlier commit (5.13): > > a358f40600b3 ("once: implement DO_ONCE_LITE for non-fast-path "do once" functionality") > > Modifies all the pr_*_once() calls to always return true claiming > that no caller is ever checking the return value of the functions. > > This is why we are seeing the callstack printed without the > associated printk() msg. Extract the ONCE_IF(cond) part into __ONCE_LTE_IF() and use that to implement DO_ONCE_LITE_IF() and fix the extable code. Fixes: a358f40600b3 ("once: implement DO_ONCE_LITE for non-fast-path "do once" functionality") Reported-by: Stephane Eranian Signed-off-by: Peter Zijlstra (Intel) Tested-by: Stephane Eranian Link: https://lkml.kernel.org/r/YqyVFsbviKjVGGZ9@worktop.programming.kicks-ass.net

once: implement DO_ONCE_LITE for non-fast-path "do once" functionality

2021-06-28T22:54:57+00:00

Certain uses of "do once" functionality reside outside of fast path, and so do not require jump label patching via static keys, making existing DO_ONCE undesirable in such cases. Replace uses of __section(".data.once") with DO_ONCE_LITE(_IF)? This patch changes the return values of xfs_printk_once, printk_once, and printk_deferred_once. Before, they returned whether the print was performed, but now, they always return true. This is okay because the return values of the following macros are entirely ignored throughout the kernel: - xfs_printk_once - xfs_warn_once - xfs_notice_once - xfs_info_once - printk_once - pr_emerg_once - pr_alert_once - pr_crit_once - pr_err_once - pr_warn_once - pr_notice_once - pr_info_once - pr_devel_once - pr_debug_once - printk_deferred_once - orc_warn Changes v3: - Expand commit message to explain why changing return values of xfs_printk_once, printk_once, printk_deferred_once is benign v2: - Fix i386 build warnings Signed-off-by: Tanner Love Acked-by: Eric Dumazet Acked-by: Mahesh Bandewar Acked-by: Steven Rostedt (VMware) Signed-off-by: David S. Miller