linux-kernel - Re: [PATCH 1/4] module: Add module_subinit{_noexit} and module

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Message-ID: <4570c972-de09-4818-bd1b-3112f651b49d@mbosol.com>
Date: Tue, 23 Jul 2024 12:58:10 +0300
From: Mika Penttilä <mika.penttila@...sol.com>
To: Youling Tang <youling.tang@...ux.dev>, Arnd Bergmann <arnd@...db.de>,
 Luis Chamberlain <mcgrof@...nel.org>, Chris Mason <clm@...com>,
 Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
 tytso@....edu, Andreas Dilger <adilger.kernel@...ger.ca>,
 Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
 Christoph Hellwig <hch@...radead.org>
Cc: linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-modules@...r.kernel.org, linux-btrfs@...r.kernel.org,
 linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
 Youling Tang <tangyouling@...inos.cn>
Subject: Re: [PATCH 1/4] module: Add module_subinit{_noexit} and
 module_subeixt helper macros


On 7/23/24 11:32, Youling Tang wrote:
> From: Youling Tang <tangyouling@...inos.cn>
>
> In theory init/exit should match their sequence, thus normally they should
> look like this:
> -------------------------+------------------------
>     init_A();            |
>     init_B();            |
>     init_C();            |
>                          |   exit_C();
>                          |   exit_B();
>                          |   exit_A();
>
> Providing module_subinit{_noexit} and module_subeixt helps macros ensure
> that modules init/exit match their order, while also simplifying the code.
>
> The three macros are defined as follows:
> - module_subinit(initfn, exitfn,rollback)
> - module_subinit_noexit(initfn, rollback)
> - module_subexit(rollback)
>
> `initfn` is the initialization function and `exitfn` is the corresponding
> exit function.
>
> Signed-off-by: Youling Tang <tangyouling@...inos.cn>
> ---
>  include/asm-generic/vmlinux.lds.h |  5 +++
>  include/linux/init.h              | 62 ++++++++++++++++++++++++++++++-
>  include/linux/module.h            | 22 +++++++++++
>  3 files changed, 88 insertions(+), 1 deletion(-)
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 677315e51e54..48ccac7c6448 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -927,6 +927,10 @@
>  		INIT_CALLS_LEVEL(7)					\
>  		__initcall_end = .;
>  
> +#define SUBINIT_CALL							\
> +		*(.subinitcall.init)					\
> +		*(.subexitcall.exit)
> +
>  #define CON_INITCALL							\
>  	BOUNDED_SECTION_POST_LABEL(.con_initcall.init, __con_initcall, _start, _end)
>  
> @@ -1155,6 +1159,7 @@
>  		INIT_DATA						\
>  		INIT_SETUP(initsetup_align)				\
>  		INIT_CALLS						\
> +		SUBINIT_CALL						\
>  		CON_INITCALL						\
>  		INIT_RAM_FS						\
>  	}
> diff --git a/include/linux/init.h b/include/linux/init.h
> index ee1309473bc6..e8689ff2cb6c 100644
> --- a/include/linux/init.h
> +++ b/include/linux/init.h
> @@ -55,6 +55,9 @@
>  #define __exitdata	__section(".exit.data")
>  #define __exit_call	__used __section(".exitcall.exit")
>  
> +#define __subinit_call	__used __section(".subinitcall.init")
> +#define __subexit_call	__used __section(".subexitcall.exit")
> +
>  /*
>   * modpost check for section mismatches during the kernel build.
>   * A section mismatch happens when there are references from a
> @@ -115,6 +118,9 @@
>  typedef int (*initcall_t)(void);
>  typedef void (*exitcall_t)(void);
>  
> +typedef int (*subinitcall_t)(void);
> +typedef void (*subexitcall_t)(void);
> +
>  #ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
>  typedef int initcall_entry_t;
>  
> @@ -183,7 +189,61 @@ extern struct module __this_module;
>  #endif
>  
>  #endif
> -  
> +
> +#ifndef __ASSEMBLY__
> +struct subexitcall_rollback {
> +	/*
> +	 * Records the address of the first sub-initialization function in the
> +	 * ".subexitcall.exit" section
> +	 */
> +	unsigned long first_addr;
> +	int ncalls;
> +};
> +
> +static inline void __subexitcall_rollback(struct subexitcall_rollback *r)
> +{
> +	unsigned long addr = r->first_addr - sizeof(r->first_addr) * (r->ncalls - 1);
> +
> +	for (; r->ncalls--; addr += sizeof(r->first_addr)) {
> +		unsigned long *tmp = (void *)addr;
> +		subexitcall_t fn = (subexitcall_t)*tmp;
> +		fn();
> +	}
> +}

How does this guarantee the exit calls match sequence? Are you assuming
linker puts exit functions in reverse order?


--Mika