Re: [PATCH 1/2] kexec: Add permission notifier chain for kexec operations

[Mukesh R <mrathor@linux.microsoft.com>]

On 1/28/26 09:42, Stanislav Kinsburskii wrote:
> Add a blocking notifier chain to allow subsystems to be notified
> before kexec execution. This enables modules to perform necessary
> cleanup or validation before the system transitions to a new kernel or
> block kexec if not possible under current conditions.
> 
> Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
> ---
>   include/linux/kexec.h |    6 ++++++
>   kernel/kexec_core.c   |   24 ++++++++++++++++++++++++
>   2 files changed, 30 insertions(+)
> 
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index ff7e231b0485..311037d30f9e 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -35,6 +35,7 @@ extern note_buf_t __percpu *crash_notes;
>   #include <linux/ioport.h>
>   #include <linux/module.h>
>   #include <linux/highmem.h>
> +#include <linux/notifier.h>
>   #include <asm/kexec.h>
>   #include <linux/crash_core.h>
>   
> @@ -532,10 +533,13 @@ extern bool kexec_file_dbg_print;
>   
>   extern void *kimage_map_segment(struct kimage *image, unsigned long addr, unsigned long size);
>   extern void kimage_unmap_segment(void *buffer);
> +extern int kexec_block_notifier_register(struct notifier_block *nb);
> +extern int kexec_block_notifier_unregister(struct notifier_block *nb);
>   #else /* !CONFIG_KEXEC_CORE */
>   struct pt_regs;
>   struct task_struct;
>   struct kimage;
> +struct notifier_block;
>   static inline void __crash_kexec(struct pt_regs *regs) { }
>   static inline void crash_kexec(struct pt_regs *regs) { }
>   static inline int kexec_should_crash(struct task_struct *p) { return 0; }
> @@ -543,6 +547,8 @@ static inline int kexec_crash_loaded(void) { return 0; }
>   static inline void *kimage_map_segment(struct kimage *image, unsigned long addr, unsigned long size)
>   { return NULL; }
>   static inline void kimage_unmap_segment(void *buffer) { }
> +static inline int kexec_block_notifier_register(struct notifier_block *nb) { }
> +static inline int kexec_block_notifier_unregister(struct notifier_block *nb) { }
>   #define kexec_in_progress false
>   #endif /* CONFIG_KEXEC_CORE */
>   
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index 0f92acdd354d..1e86a6f175f0 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -57,6 +57,20 @@ bool kexec_in_progress = false;
>   
>   bool kexec_file_dbg_print;
>   
> +static BLOCKING_NOTIFIER_HEAD(kexec_block_list);
> +
> +int kexec_block_notifier_register(struct notifier_block *nb)
> +{
> +	return blocking_notifier_chain_register(&kexec_block_list, nb);
> +}
> +EXPORT_SYMBOL_GPL(kexec_block_notifier_register);
> +
> +int kexec_block_notifier_unregister(struct notifier_block *nb)
> +{
> +	return blocking_notifier_chain_unregister(&kexec_block_list, nb);
> +}
> +EXPORT_SYMBOL_GPL(kexec_block_notifier_unregister);
> +
>   /*
>    * When kexec transitions to the new kernel there is a one-to-one
>    * mapping between physical and virtual addresses.  On processors
> @@ -1124,6 +1138,12 @@ bool kexec_load_permitted(int kexec_image_type)
>   	return true;
>   }
>   
> +static int kexec_check_blockers(void)
> +{
> +	/* Notify subsystems of impending kexec */
> +	return blocking_notifier_call_chain(&kexec_block_list, 0, NULL);
> +}
> +
>   /*
>    * Move into place and start executing a preloaded standalone
>    * executable.  If nothing was preloaded return an error.
> @@ -1139,6 +1159,10 @@ int kernel_kexec(void)
>   		goto Unlock;
>   	}
>   
> +	error = kexec_check_blockers();

This could take a long time, and I am not sure if it's a good idea
to stall kexec with such dependencies.

Thanks,
-Mukesh


> +	if (error)
> +		goto Unlock;
> +
>   	error = liveupdate_reboot();
>   	if (error)
>   		goto Unlock;
> 
>