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Fri, 23 Jan 2026 09:42:54 -0800 (PST) MIME-Version: 1.0 References: <70dcf80f79ecd00a750ea17101061b0949119429.1769086312.git.lorenzo.stoakes@oracle.com> In-Reply-To: From: Suren Baghdasaryan Date: Fri, 23 Jan 2026 09:42:43 -0800 X-Gm-Features: AZwV_Qg0XqJp6LB6ClHaUtMVJzUsaWRJQOHROvVx-k5EXeTYGcGYUgT45CfCEsU Message-ID: Subject: Re: [PATCH RESEND v3 08/10] mm/vma: improve and document __is_vma_write_locked() To: Vlastimil Babka Cc: Lorenzo Stoakes , Andrew Morton , David Hildenbrand , "Liam R . Howlett" , Mike Rapoport , Michal Hocko , Shakeel Butt , Jann Horn , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng , Waiman Long , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 0AE7710000A X-Stat-Signature: ja64iupt888zcsxh4qh3gnta1zbqn11t X-Rspam-User: X-HE-Tag: 1769190175-287432 X-HE-Meta: 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 6ZGX5+/j EuPl0k7gvit67ylKwlQMdOff9Gutks0Cd0sE0mk1VLGSspyutgOgLz0F1AcgiRA9csL0sJPfKbjCOeMZPmbYbQzrkpUMEqh8fTb1vwJzclgNj4a/SNa72Vp73OPuwRApOlY4bIaXC7go00FO/8FaYjXg098yi1LCS+bk8fIGOuve7dws3C8j3XSng95pHZNUzCakAR3uNKdm743NhG2q5RjeIW+JJNWictoV+gCU2+ANAaK2s0pT93Wk4o1jcW4TAncpXMbpYYx1hAYbRJuzNgc5ZJ48gE7FBRIvNb1JF1hnDGBeu6rzL5WFvFHqReN4mhUaN4oJ3PaXclrROS7wdLPlAMM+NrF2/+wVc0yAnZxrPaiy9gBNgBiH2G0PRciinXfUK X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jan 23, 2026 at 8:21=E2=80=AFAM Vlastimil Babka wr= ote: > > On 1/22/26 22:55, Suren Baghdasaryan wrote: > > On Thu, Jan 22, 2026 at 5:02=E2=80=AFAM Lorenzo Stoakes > > wrote: > >> > >> The function is a little confusing, clean it up a little then add a > >> descriptive comment. > > > > I appreciate the descriptive comment but what exactly was confusing in > > this function? > > > >> > >> No functional change intended. > >> > >> Signed-off-by: Lorenzo Stoakes > >> --- > >> include/linux/mmap_lock.h | 23 ++++++++++++++++++----- > >> 1 file changed, 18 insertions(+), 5 deletions(-) > >> > >> diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h > >> index 873bc5f3c97c..b00d34b5ad10 100644 > >> --- a/include/linux/mmap_lock.h > >> +++ b/include/linux/mmap_lock.h > >> @@ -252,17 +252,30 @@ static inline void vma_end_read(struct vm_area_s= truct *vma) > >> vma_refcount_put(vma); > >> } > >> > >> -/* WARNING! Can only be used if mmap_lock is expected to be write-loc= ked */ > >> -static inline bool __is_vma_write_locked(struct vm_area_struct *vma, = unsigned int *mm_lock_seq) > >> +/* > >> + * Determine whether a VMA is write-locked. Must be invoked ONLY if t= he mmap > >> + * write lock is held. > >> + * > >> + * Returns true if write-locked, otherwise false. > >> + * > >> + * Note that mm_lock_seq is updated only if the VMA is NOT write-lock= ed. > > Could it also say to what it's updated to? Or is it too obvious? > > > > > True, this does not result in a functional change because we do not > > use mm_lock_seq if __is_vma_write_locked() succeeds. However this > > seems to add additional gotcha that you need to remember. Any reason > > why? > > Actually I wonder if it's really worth returning the mm_lock_seq and pass= ing > it to __vma_start_write(), which could just determine it on its own. It > would simplify things. That looks fine to me and indeed would simplify things... Yes, please! > > >> + */ > >> +static inline bool __is_vma_write_locked(struct vm_area_struct *vma, > >> + unsigned int *mm_lock_seq) > >> { > >> - mmap_assert_write_locked(vma->vm_mm); > >> + struct mm_struct *mm =3D vma->vm_mm; > >> + const unsigned int seq =3D mm->mm_lock_seq.sequence; > >> + > >> + mmap_assert_write_locked(mm); > >> > >> /* > >> * current task is holding mmap_write_lock, both vma->vm_lock_= seq and > >> * mm->mm_lock_seq can't be concurrently modified. > >> */ > >> - *mm_lock_seq =3D vma->vm_mm->mm_lock_seq.sequence; > >> - return (vma->vm_lock_seq =3D=3D *mm_lock_seq); > >> + if (vma->vm_lock_seq =3D=3D seq) > >> + return true; > >> + *mm_lock_seq =3D seq; > >> + return false; > >> } > >> > >> int __vma_start_write(struct vm_area_struct *vma, unsigned int mm_loc= k_seq, > >> -- > >> 2.52.0 >