linux-kernel - Re: [PATCH -next] kdb: Use newer api for tasklist scanning

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Message-ID: <20200907134614.guc4tzj3knnihbe4@holly.lan>
Date:   Mon, 7 Sep 2020 14:46:14 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     jason.wessel@...driver.com, dianders@...omium.org, oleg@...hat.com,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH -next] kdb: Use newer api for tasklist scanning

On Mon, Aug 31, 2020 at 12:34:35PM -0700, Davidlohr Bueso wrote:
> This kills the custom kdb_do_each_thread/kdb_while_each_thread
> calls used in kdb to iterate through all tasks. It is obsolete
> and racy to use tsk->thread_group, although in this particular

No objections to the change but kdb doesn't use tsk->thread_group,
it uses do_each_thread/while_each_thread. Can we change this to
say that is osbsolete and racy to use while_each_thread() (that's
pretty much what the description of the patch that introduced
for_each_thread said)?

Additionally the debug_core uses do_each_thread/while_each_thread.
Presumably that would like to be changed as well?


Daniel.



> case there is no concurrency so it doesn't matter. Still, lets
> trivially replace it for the newer one, maintaining semantics,
> of course.
> 
> Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
> ---
>  kernel/debug/kdb/kdb_bt.c      | 4 ++--
>  kernel/debug/kdb/kdb_main.c    | 8 ++++----
>  kernel/debug/kdb/kdb_private.h | 4 ----
>  3 files changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/kernel/debug/kdb/kdb_bt.c b/kernel/debug/kdb/kdb_bt.c
> index 18e03aba2cfc..1f9f0e47aeda 100644
> --- a/kernel/debug/kdb/kdb_bt.c
> +++ b/kernel/debug/kdb/kdb_bt.c
> @@ -149,14 +149,14 @@ kdb_bt(int argc, const char **argv)
>  				return 0;
>  		}
>  		/* Now the inactive tasks */
> -		kdb_do_each_thread(g, p) {
> +		for_each_process_thread(g, p) {
>  			if (KDB_FLAG(CMD_INTERRUPT))
>  				return 0;
>  			if (task_curr(p))
>  				continue;
>  			if (kdb_bt1(p, mask, btaprompt))
>  				return 0;
> -		} kdb_while_each_thread(g, p);
> +		}
>  	} else if (strcmp(argv[0], "btp") == 0) {
>  		struct task_struct *p;
>  		unsigned long pid;
> diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
> index 5c7949061671..930ac1b25ec7 100644
> --- a/kernel/debug/kdb/kdb_main.c
> +++ b/kernel/debug/kdb/kdb_main.c
> @@ -2299,10 +2299,10 @@ void kdb_ps_suppressed(void)
>  		if (kdb_task_state(p, mask_I))
>  			++idle;
>  	}
> -	kdb_do_each_thread(g, p) {
> +	for_each_process_thread(g, p) {
>  		if (kdb_task_state(p, mask_M))
>  			++daemon;
> -	} kdb_while_each_thread(g, p);
> +	}
>  	if (idle || daemon) {
>  		if (idle)
>  			kdb_printf("%d idle process%s (state I)%s\n",
> @@ -2370,12 +2370,12 @@ static int kdb_ps(int argc, const char **argv)
>  	}
>  	kdb_printf("\n");
>  	/* Now the real tasks */
> -	kdb_do_each_thread(g, p) {
> +	for_each_process_thread(g, p) {
>  		if (KDB_FLAG(CMD_INTERRUPT))
>  			return 0;
>  		if (kdb_task_state(p, mask))
>  			kdb_ps1(p);
> -	} kdb_while_each_thread(g, p);
> +	}
>  
>  	return 0;
>  }
> diff --git a/kernel/debug/kdb/kdb_private.h b/kernel/debug/kdb/kdb_private.h
> index 2e296e4a234c..a4281fb99299 100644
> --- a/kernel/debug/kdb/kdb_private.h
> +++ b/kernel/debug/kdb/kdb_private.h
> @@ -230,10 +230,6 @@ extern struct task_struct *kdb_curr_task(int);
>  
>  #define kdb_task_has_cpu(p) (task_curr(p))
>  
> -/* Simplify coexistence with NPTL */
> -#define	kdb_do_each_thread(g, p) do_each_thread(g, p)
> -#define	kdb_while_each_thread(g, p) while_each_thread(g, p)
> -
>  #define GFP_KDB (in_interrupt() ? GFP_ATOMIC : GFP_KERNEL)
>  
>  extern void *debug_kmalloc(size_t size, gfp_t flags);
> -- 
> 2.26.2