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X-Authority-Analysis: v=2.4 cv=dY2NHHXe c=1 sm=1 tr=0 ts=697734e0 cx=c_pps a=OOZaFjgC48PWsiFpTAqLcw==:117 a=OOZaFjgC48PWsiFpTAqLcw==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=vUbySO9Y5rIA:10 a=GoEa3M9JfhUA:10 a=VkNPw1HP01LnGYTKEx00:22 a=yPCof4ZbAAAA:8 a=1XWaLZrsAAAA:8 a=DPStYy7rvKqjGcsp66cA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: cvuo5s02D_di2c32dEn2aHVxipqCw6cV X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTI2MDA4MSBTYWx0ZWRfX71u8IeRYlNr7 VV3OyAj9M2OBnajNubBIneasi4Xo2xKJzT5ODtjgGpjeL9+3ePQmNX6f4TstsiVO5+hdWCp8V89 S8hNrraLQDiyrSueJEqiDyemSqAGtozMJMFTfutFokGVkZDS2qVv5ErcwIEGSuoQQff6I7fk8Gp nElwCtCxLdISEv3MIAs6p77mYddtypolIgy2v8Qf8e3qJ/CxTlepz3ToiVTWTHx/4Ry+RV3g8sG PFGkCoa+DV1BwpionqhIVvUG7GCggFAMp5pzn3nkhS/pOWc+WinTO4IbDWdHLlomaKdwHHEqTH0 7u9Eg2zfjtKyyl/me1VSv++D5KsNKVC1U4rXA5jRr+9M4Ik7H6FDhmW2ZH1vJ60m0gP9KXaAk7K 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I9XO6JUF59RPJNV90smlWo6RdUCzxVnhFNlEXbxKfI7qQX9noOWGyoCWVvONGennxqxBC4XHyL6ouKTwt1xSDAhd/syyuBBClMr7SjdqcsH942AaX9GRRxruR5dZHTRFy1Z4RBchm36XtE5PUqv3OhGPA3NdUuyCbjAio 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: Andrew - could you fix up the typo below? If a pain I can send a fix-patch thanks :) On Sun, Jan 25, 2026 at 09:15:04PM -0800, Suren Baghdasaryan wrote: > On Fri, Jan 23, 2026 at 12:12 PM Lorenzo Stoakes > wrote: > > > > The possible vma->vm_refcnt values are confusing and vague, explain in > > detail what these can be in a comment describing the vma->vm_refcnt field > > and reference this comment in various places that read/write this field. > > > > No functional change intended. > > > > Signed-off-by: Lorenzo Stoakes > > One nit, otherwise LGTM: > > Reviewed-by: Suren Baghdasaryan Thanks! > > > --- > > include/linux/mm_types.h | 42 +++++++++++++++++++++++++++++++++++++-- > > include/linux/mmap_lock.h | 7 +++++++ > > mm/mmap_lock.c | 6 ++++++ > > 3 files changed, 53 insertions(+), 2 deletions(-) > > > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > > index bdbf17c4f26b..12281a1128c9 100644 > > --- a/include/linux/mm_types.h > > +++ b/include/linux/mm_types.h > > @@ -758,7 +758,8 @@ static inline struct anon_vma_name *anon_vma_name_alloc(const char *name) > > * set the VM_REFCNT_EXCLUDE_READERS_FLAG in vma->vm_refcnt to indiciate to > > * vma_start_read() that the reference count should be left alone. > > * > > - * Once the operation is complete, this value is subtracted from vma->vm_refcnt. > > + * See the comment describing vm_refcnt in vm_area_struct for details as to > > + * which values the VMA reference count can be. > > */ > > #define VM_REFCNT_EXCLUDE_READERS_BIT (30) > > #define VM_REFCNT_EXCLUDE_READERS_FLAG (1U << VM_REFCNT_EXCLUDE_READERS_BIT) > > @@ -989,7 +990,44 @@ struct vm_area_struct { > > struct vma_numab_state *numab_state; /* NUMA Balancing state */ > > #endif > > #ifdef CONFIG_PER_VMA_LOCK > > - /* Unstable RCU readers are allowed to read this. */ > > + /* > > + * Used to keep track of firstly, whether the VMA is attached, secondly, > > + * if attached, how many read locks are taken, and thirdly, if the > > + * VM_REFCNT_EXCLUDE_READERS_FLAG is set, whether any read locks held > > + * are currently in the process of being excluded. > > + * > > + * This value can be equal to: > > + * > > + * 0 - Detached. IMPORTANT: when the refcnt is zero, readers cannot > > + * increment it. > > + * > > + * 1 - Attached and either unlocked or write-locked. Write locks are > > + * identified via __is_vma_write_locked() which checks for equality of > > + * vma->vm_lock_seq and mm->mm_lock_seq. > > + * > > + * >1, < VM_REFCNT_EXCLUDE_READERS_FLAG - Read-locked or (unlikely) > > + * write-locked with other threads having temporarily incremented the > > + * reference count prior to determining it is write-locked and > > + * decrementing it again. > > + * > > + * VM_REFCNT_EXCLUDE_READERS_FLAG - Detached, pending > > + * __vma_exit_locked() completion which will decrement the reference > > + * count to zero. IMPORTANT - at this stage no further readers can > > + * increment the reference count. It can only be reduced. > > + * > > + * VM_REFCNT_EXCLUDE_READERS_FLAG + 1 - A thread is either write-locking > > + * an attached VMA and has yet to invoke __vma_exit_locked(), OR a > > + * thread is detaching a VMA and is waiting on a single spurious reader > > + * in order to decrement the reference count. IMPORTANT - as above, no > > + * further readers can increment the reference count. > > + * > > + * > VM_REFCNT_EXCLUDE_READERS_FLAG + 1 - A thread is either > > + * write-locking or detaching a VMA is waiting on readers to > > + * exit. IMPORTANT - as above, no ruther readers can increment the > > s/ruther/further You're depriving newer kernel people of typo fixup series which is, of course, why I leave these in patches *ahem* :P Thanks, hopefully Andrew can fix up trivially! Cheers, Lorenzo