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AJvYcCVNXt7Cy2pwHYQqzSm8e+tE+ajxHQ95SFP2guqMlkmrkmOT+XXPouH+Teh9w3iisrlspfOcAWNPug==@kvack.org X-Gm-Message-State: AOJu0Yyn3KYeoFsryQgXDyv+VIVVxiOidGvzY6JD367HUp7FKCxkeve3 PeaAZwuL5spRDX5KgF2YkToPZNsXLhmYjxI0TCYr957OFe05tb9sW40aWS/tsgWPKw2JfNmpOx/ Xnw== X-Google-Smtp-Source: AGHT+IEyLwXvDXLnYSqPv5azfkHnhcNjKGMYmPlWD8dNq1sLWn2jjgJONFBDd+BEsDvXmrivA7Y5d4vobs8= X-Received: from surenb-desktop.mtv.corp.google.com ([2a00:79e0:2e3f:8:af45:bbc1:fc75:e695]) (user=surenb job=sendgmr) by 2002:a25:aa22:0:b0:e2e:3401:ea0f with SMTP id 3f1490d57ef6-e38cb70b565mr451276.7.1732061312659; Tue, 19 Nov 2024 16:08:32 -0800 (PST) Date: Tue, 19 Nov 2024 16:08:22 -0800 In-Reply-To: <20241120000826.335387-1-surenb@google.com> Mime-Version: 1.0 References: <20241120000826.335387-1-surenb@google.com> X-Mailer: git-send-email 2.47.0.338.g60cca15819-goog Message-ID: <20241120000826.335387-2-surenb@google.com> Subject: [PATCH v4 1/5] mm: introduce vma_start_read_locked{_nested} helpers From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: willy@infradead.org, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, corbet@lwn.net, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com, surenb@google.com X-Rspam-User: X-Rspamd-Queue-Id: 265B340007 X-Rspamd-Server: rspam01 X-Stat-Signature: asud863wqdx9ncp935x4fisdi5i3ppxj X-HE-Tag: 1732061243-335871 X-HE-Meta: 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 NQSHg0Ke 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 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: Introduce helper functions which can be used to read-lock a VMA when holding mmap_lock for read. Replace direct accesses to vma->vm_lock with these new helpers. Signed-off-by: Suren Baghdasaryan Reviewed-by: Lorenzo Stoakes Reviewed-by: Davidlohr Bueso Reviewed-by: Shakeel Butt --- include/linux/mm.h | 24 ++++++++++++++++++++++++ mm/userfaultfd.c | 22 +++++----------------- 2 files changed, 29 insertions(+), 17 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index fecd47239fa9..1ba2e480ae63 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -722,6 +722,30 @@ static inline bool vma_start_read(struct vm_area_struct *vma) return true; } +/* + * Use only while holding mmap read lock which guarantees that locking will not + * fail (nobody can concurrently write-lock the vma). vma_start_read() should + * not be used in such cases because it might fail due to mm_lock_seq overflow. + * This functionality is used to obtain vma read lock and drop the mmap read lock. + */ +static inline void vma_start_read_locked_nested(struct vm_area_struct *vma, int subclass) +{ + mmap_assert_locked(vma->vm_mm); + down_read_nested(&vma->vm_lock->lock, subclass); +} + +/* + * Use only while holding mmap read lock which guarantees that locking will not + * fail (nobody can concurrently write-lock the vma). vma_start_read() should + * not be used in such cases because it might fail due to mm_lock_seq overflow. + * This functionality is used to obtain vma read lock and drop the mmap read lock. + */ +static inline void vma_start_read_locked(struct vm_area_struct *vma) +{ + mmap_assert_locked(vma->vm_mm); + down_read(&vma->vm_lock->lock); +} + static inline void vma_end_read(struct vm_area_struct *vma) { rcu_read_lock(); /* keeps vma alive till the end of up_read */ diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 60a0be33766f..87db4b32b82a 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -84,16 +84,8 @@ static struct vm_area_struct *uffd_lock_vma(struct mm_struct *mm, mmap_read_lock(mm); vma = find_vma_and_prepare_anon(mm, address); - if (!IS_ERR(vma)) { - /* - * We cannot use vma_start_read() as it may fail due to - * false locked (see comment in vma_start_read()). We - * can avoid that by directly locking vm_lock under - * mmap_lock, which guarantees that nobody can lock the - * vma for write (vma_start_write()) under us. - */ - down_read(&vma->vm_lock->lock); - } + if (!IS_ERR(vma)) + vma_start_read_locked(vma); mmap_read_unlock(mm); return vma; @@ -1476,14 +1468,10 @@ static int uffd_move_lock(struct mm_struct *mm, mmap_read_lock(mm); err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap); if (!err) { - /* - * See comment in uffd_lock_vma() as to why not using - * vma_start_read() here. - */ - down_read(&(*dst_vmap)->vm_lock->lock); + vma_start_read_locked(*dst_vmap); if (*dst_vmap != *src_vmap) - down_read_nested(&(*src_vmap)->vm_lock->lock, - SINGLE_DEPTH_NESTING); + vma_start_read_locked_nested(*src_vmap, + SINGLE_DEPTH_NESTING); } mmap_read_unlock(mm); return err;