linux-kernel - Re: [PATCH 13/41] mm: introduce vma->vm

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Y8a6DhA6o3jcZaM3@dhcp22.suse.cz>
Date:   Tue, 17 Jan 2023 16:09:02 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, michel@...pinasse.org,
        jglisse@...gle.com, vbabka@...e.cz, hannes@...xchg.org,
        mgorman@...hsingularity.net, dave@...olabs.net,
        willy@...radead.org, liam.howlett@...cle.com, peterz@...radead.org,
        ldufour@...ux.ibm.com, laurent.dufour@...ibm.com,
        paulmck@...nel.org, luto@...nel.org, songliubraving@...com,
        peterx@...hat.com, david@...hat.com, dhowells@...hat.com,
        hughd@...gle.com, bigeasy@...utronix.de, kent.overstreet@...ux.dev,
        punit.agrawal@...edance.com, lstoakes@...il.com,
        peterjung1337@...il.com, rientjes@...gle.com,
        axelrasmussen@...gle.com, joelaf@...gle.com, minchan@...gle.com,
        jannh@...gle.com, shakeelb@...gle.com, tatashin@...gle.com,
        edumazet@...gle.com, gthelen@...gle.com, gurua@...gle.com,
        arjunroy@...gle.com, soheil@...gle.com, hughlynch@...gle.com,
        leewalsh@...gle.com, posk@...gle.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 13/41] mm: introduce vma->vm_flags modifier functions

On Mon 09-01-23 12:53:08, Suren Baghdasaryan wrote:
> To keep vma locking correctness when vm_flags are modified, add modifier
> functions to be used whenever flags are updated.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> ---
>  include/linux/mm.h       | 38 ++++++++++++++++++++++++++++++++++++++
>  include/linux/mm_types.h |  8 +++++++-
>  2 files changed, 45 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ec2c4c227d51..35cf0a6cbcc2 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -702,6 +702,44 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
>  	vma_init_lock(vma);
>  }
>  
> +/* Use when VMA is not part of the VMA tree and needs no locking */
> +static inline
> +void init_vm_flags(struct vm_area_struct *vma, unsigned long flags)
> +{
> +	WRITE_ONCE(vma->vm_flags, flags);
> +}

Why do we need WRITE_ONCE here? Isn't vma invisible during its
initialization?

> +
> +/* Use when VMA is part of the VMA tree and needs appropriate locking */
> +static inline
> +void reset_vm_flags(struct vm_area_struct *vma, unsigned long flags)
> +{
> +	vma_write_lock(vma);
> +	init_vm_flags(vma, flags);
> +}
> +
> +static inline
> +void set_vm_flags(struct vm_area_struct *vma, unsigned long flags)
> +{
> +	vma_write_lock(vma);
> +	vma->vm_flags |= flags;
> +}
> +
> +static inline
> +void clear_vm_flags(struct vm_area_struct *vma, unsigned long flags)
> +{
> +	vma_write_lock(vma);
> +	vma->vm_flags &= ~flags;
> +}
> +
> +static inline
> +void mod_vm_flags(struct vm_area_struct *vma,
> +		  unsigned long set, unsigned long clear)
> +{
> +	vma_write_lock(vma);
> +	vma->vm_flags |= set;
> +	vma->vm_flags &= ~clear;
> +}
> +

This is rather unusual pattern. There is no note about locking involved
in the naming and also why is the locking part of this interface in the
first place? I can see reason for access functions to actually check for
lock asserts.
-- 
Michal Hocko
SUSE Labs