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AJvYcCXYLTuq2gIGc8ZlNitJX/+27WX2AZnyr2SXsoRmeKYHHDi2TuoS3n5GdzQodR8Ab+OSxc/loqLxug==@kvack.org X-Gm-Message-State: AOJu0YzSOflwY/RSz1XmPYNruBdJ68S9tAN3zX1PdakR4VqF00p+2nMz l3Sg8WeW7f4XdUZN3pIJjVUuJLn+SwbXQo8o1CAIfSXNKkS/rw0oqbkp/gc4M9c99uY0tQL7zLp wtg== X-Google-Smtp-Source: AGHT+IFvP7Rtv2Mvdra3Yg1NiqesqrI7PbBRDKrXPHHWmHQO1TyYtp4d3ffasZylr6rr8GVtjs5kwYbmVJQ= X-Received: from pfbgd3.prod.google.com ([2002:a05:6a00:8303:b0:730:8c7f:979]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:c997:b0:1ee:3b53:b77f with SMTP id adf61e73a8af0-1ee6b4013abmr9718076637.37.1739486834016; Thu, 13 Feb 2025 14:47:14 -0800 (PST) Date: Thu, 13 Feb 2025 14:46:44 -0800 In-Reply-To: <20250213224655.1680278-1-surenb@google.com> Mime-Version: 1.0 References: <20250213224655.1680278-1-surenb@google.com> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog Message-ID: <20250213224655.1680278-8-surenb@google.com> Subject: [PATCH v10 07/18] mm: allow vma_start_read_locked/vma_start_read_locked_nested to fail From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: peterz@infradead.org, willy@infradead.org, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, david.laight.linux@gmail.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, lokeshgidra@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, klarasmodin@gmail.com, richard.weiyang@gmail.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: 27D0D140009 X-Rspamd-Server: rspam12 X-Stat-Signature: af66qbw1wm91gc359a3smazuzb7efs6u X-HE-Tag: 1739486834-581325 X-HE-Meta: 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 TnmenAVu 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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: With upcoming replacement of vm_lock with vm_refcnt, we need to handle a possibility of vma_start_read_locked/vma_start_read_locked_nested failing due to refcount overflow. Prepare for such possibility by changing these APIs and adjusting their users. Signed-off-by: Suren Baghdasaryan Cc: Lokesh Gidra --- Changes since v9 [1]: - Refactor the code, per Lorenzo Stoakes - Remove Vlastimil's Acked-by since code is changed [1] https://lore.kernel.org/all/20250111042604.3230628-8-surenb@google.com/ include/linux/mm.h | 6 ++++-- mm/userfaultfd.c | 30 +++++++++++++++++++++++------- 2 files changed, 27 insertions(+), 9 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 1b8e72888124..7fa7c39162fd 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -747,10 +747,11 @@ static inline bool vma_start_read(struct vm_area_struct *vma) * 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) +static inline bool 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); + return true; } /* @@ -759,10 +760,11 @@ static inline void vma_start_read_locked_nested(struct vm_area_struct *vma, int * 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) +static inline bool vma_start_read_locked(struct vm_area_struct *vma) { mmap_assert_locked(vma->vm_mm); down_read(&vma->vm_lock.lock); + return true; } static inline void vma_end_read(struct vm_area_struct *vma) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 4527c385935b..867898c4e30b 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -84,8 +84,12 @@ 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)) - vma_start_read_locked(vma); + if (!IS_ERR(vma)) { + bool locked = vma_start_read_locked(vma); + + if (!locked) + vma = ERR_PTR(-EAGAIN); + } mmap_read_unlock(mm); return vma; @@ -1482,12 +1486,24 @@ 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) { - vma_start_read_locked(*dst_vmap); - if (*dst_vmap != *src_vmap) - vma_start_read_locked_nested(*src_vmap, - SINGLE_DEPTH_NESTING); + if (err) + goto out; + + if (!vma_start_read_locked(*dst_vmap)) { + err = -EAGAIN; + goto out; } + + /* Nothing further to do if both vmas are locked. */ + if (*dst_vmap == *src_vmap) + goto out; + + if (!vma_start_read_locked_nested(*src_vmap, SINGLE_DEPTH_NESTING)) { + /* Undo dst_vmap locking if src_vmap failed to lock */ + vma_end_read(*dst_vmap); + err = -EAGAIN; + } +out: mmap_read_unlock(mm); return err; }