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AJvYcCW8TlCCezFVtG/eFkqaU5ncIBbpaysSQWoA1kMgARdA9F63nCMNTo/0zRTG9P1k2OAyj0RWK2zKKQ==@kvack.org X-Gm-Message-State: AOJu0Yz+X98rRfKzh+B3FEXjAxAY6fyp3dH4/1EunO3rrZPHxSoTWkPK U5lM1DFRGMYRiYwUkAMqzJIOI8mn25Er7CWkRTIH1WeQYHtNJAYtEjxcxBKwen5Jcx9ByXdzrmh /cA== X-Google-Smtp-Source: AGHT+IH7Nd8pXV7CscbKL6Oe02lMMMIInGW3q+Det1fKSUjvn9CktAIAKXjQIOt60hBNRgC9PV8ouBWRm4Y= X-Received: from surenb-desktop.mtv.corp.google.com ([2a00:79e0:2e3f:8:bafc:6633:f766:6415]) (user=surenb job=sendgmr) by 2002:a25:9d85:0:b0:e2e:317a:d599 with SMTP id 3f1490d57ef6-e3824ac0065mr340301276.2.1731830978836; Sun, 17 Nov 2024 00:09:38 -0800 (PST) Date: Sun, 17 Nov 2024 00:09:27 -0800 In-Reply-To: <20241117080931.600731-1-surenb@google.com> Mime-Version: 1.0 References: <20241117080931.600731-1-surenb@google.com> X-Mailer: git-send-email 2.47.0.338.g60cca15819-goog Message-ID: <20241117080931.600731-2-surenb@google.com> Subject: [PATCH v3 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-Stat-Signature: tnmr4q68r9du8wgcu1fnmh6zu7tbrsgh X-Rspam-User: X-Rspamd-Queue-Id: A73501C0003 X-Rspamd-Server: rspam02 X-HE-Tag: 1731830958-564597 X-HE-Meta: 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 f0gCIL69 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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 --- 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;