linux-kernel - Re: [PATCH v2 sl-b 3/5] mm: Make mem_dump

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Date:   Wed, 9 Dec 2020 20:36:37 +0100
From:   Uladzislau Rezki <urezki@...il.com>
To:     paulmck@...nel.org
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, mingo@...nel.org, jiangshanlai@...il.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        iamjoonsoo.kim@....com, andrii@...nel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 sl-b 3/5] mm: Make mem_dump_obj() handle vmalloc()
 memory

On Tue, Dec 08, 2020 at 05:13:01PM -0800, paulmck@...nel.org wrote:
> From: "Paul E. McKenney" <paulmck@...nel.org>
> 
> This commit adds vmalloc() support to mem_dump_obj().  Note that the
> vmalloc_dump_obj() function combines the checking and dumping, in
> contrast with the split between kmem_valid_obj() and kmem_dump_obj().
> The reason for the difference is that the checking in the vmalloc()
> case involves acquiring a global lock, and redundant acquisitions of
> global locks should be avoided, even on not-so-fast paths.
> 
> Note that this change causes on-stack variables to be reported as
> vmalloc() storage from kernel_clone() or similar, depending on the degree
> of inlining that your compiler does.  This is likely more helpful than
> the earlier "non-paged (local) memory".
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: <linux-mm@...ck.org>
> Reported-by: Andrii Nakryiko <andrii@...nel.org>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---
>  include/linux/vmalloc.h |  6 ++++++
>  mm/util.c               | 12 +++++++-----
>  mm/vmalloc.c            | 12 ++++++++++++
>  3 files changed, 25 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 938eaf9..c89c2be 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -248,4 +248,10 @@ pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
>  int register_vmap_purge_notifier(struct notifier_block *nb);
>  int unregister_vmap_purge_notifier(struct notifier_block *nb);
>  
> +#ifdef CONFIG_MMU
> +bool vmalloc_dump_obj(void *object);
> +#else
> +static inline bool vmalloc_dump_obj(void *object) { return false; }
> +#endif
> +
>  #endif /* _LINUX_VMALLOC_H */
> diff --git a/mm/util.c b/mm/util.c
> index 8c2449f..ee99a0a 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -984,6 +984,12 @@ int __weak memcmp_pages(struct page *page1, struct page *page2)
>   */
>  void mem_dump_obj(void *object)
>  {
> +	if (kmem_valid_obj(object)) {
> +		kmem_dump_obj(object);
> +		return;
> +	}
> +	if (vmalloc_dump_obj(object))
> +		return;
>  	if (!virt_addr_valid(object)) {
>  		if (object == NULL)
>  			pr_cont(" NULL pointer.\n");
> @@ -993,10 +999,6 @@ void mem_dump_obj(void *object)
>  			pr_cont(" non-paged (local) memory.\n");
>  		return;
>  	}
> -	if (kmem_valid_obj(object)) {
> -		kmem_dump_obj(object);
> -		return;
> -	}
> -	pr_cont(" non-slab memory.\n");
> +	pr_cont(" non-slab/vmalloc memory.\n");
>  }
>  EXPORT_SYMBOL_GPL(mem_dump_obj);
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 6ae491a..7421719 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3431,6 +3431,18 @@ void pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
>  }
>  #endif	/* CONFIG_SMP */
>  
> +bool vmalloc_dump_obj(void *object)
> +{
> +	struct vm_struct *vm;
> +	void *objp = (void *)PAGE_ALIGN((unsigned long)object);
>
Paul, vmalloced addresses are already aligned to PAGE_SIZE, so that one
is odd.

--
Vlad Rezki