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x86/percpu: Fix "const_pcpu_hot" version generation failure

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Version generation for "const_pcpu_hot" symbol failed because genksyms
doesn't know the __seg_gs keyword. Effectively revert commit 4604c052b8
("x86/percpu: Declare const_pcpu_hot as extern const variable") and
use this_cpu_read_const() instead to avoid "sparse: dereference of
noderef expression" warning when reading const_pcpu_hot.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20231204210320.114429-1-ubizjak@gmail.com
This commit is contained in:
Uros Bizjak 2023-12-04 22:02:29 +01:00 committed by Ingo Molnar
parent fc50065325
commit 0e3703630b
3 changed files with 11 additions and 3 deletions
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5
arch/x86/include/asm/current.h
View File

@ -37,12 +37,13 @@ static_assert(sizeof(struct pcpu_hot) == 64);
DECLARE_PER_CPU_ALIGNED(struct pcpu_hot, pcpu_hot);
/* const-qualified alias to pcpu_hot, aliased by linker. */
extern const struct pcpu_hot __percpu_seg_override const_pcpu_hot;
DECLARE_PER_CPU_ALIGNED(const struct pcpu_hot __percpu_seg_override,
const_pcpu_hot);
static __always_inline struct task_struct *get_current(void)
{
if (IS_ENABLED(CONFIG_USE_X86_SEG_SUPPORT))
return const_pcpu_hot.current_task;
return this_cpu_read_const(const_pcpu_hot.current_task);
return this_cpu_read_stable(pcpu_hot.current_task);
}

7
arch/x86/include/asm/percpu.h
View File

@ -28,6 +28,7 @@
#else /* ...!ASSEMBLY */
#include <linux/build_bug.h>
#include <linux/kernel.h>
#include <linux/stringify.h>
@ -462,6 +463,7 @@ do { \
#define this_cpu_write_8(pcp, val) __raw_cpu_write(volatile, pcp, val)
#endif
#define this_cpu_read_const(pcp) __raw_cpu_read(, pcp)
#else /* CONFIG_USE_X86_SEG_SUPPORT */
#define raw_cpu_read_1(pcp) percpu_from_op(1, , "mov", pcp)
@ -486,6 +488,11 @@ do { \
#define this_cpu_write_8(pcp, val) percpu_to_op(8, volatile, "mov", (pcp), val)
#endif
/*
* The generic per-cpu infrastrucutre is not suitable for
* reading const-qualified variables.
*/
#define this_cpu_read_const(pcp) ({ BUILD_BUG(); (typeof(pcp))0; })
#endif /* CONFIG_USE_X86_SEG_SUPPORT */
#define raw_cpu_add_1(pcp, val) percpu_add_op(1, , (pcp), val)

2
arch/x86/include/asm/processor.h
View File

@ -519,7 +519,7 @@ static __always_inline unsigned long current_top_of_stack(void)
* entry trampoline.
*/
if (IS_ENABLED(CONFIG_USE_X86_SEG_SUPPORT))
return const_pcpu_hot.top_of_stack;
return this_cpu_read_const(const_pcpu_hot.top_of_stack);
return this_cpu_read_stable(pcpu_hot.top_of_stack);
}