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Howlett" , Andrew Morton , Greg Kroah-Hartman , Arnd Bergmann , Jann Horn , Suren Baghdasaryan Cc: Alex Gaynor , Boqun Feng , Gary Guo , "=?utf-8?q?Bj=C3=B6rn_Roy_Baron?=" , Benno Lossin , Andreas Hindborg , Trevor Gross , Linus Torvalds , linux-kernel@vger.kernel.org, linux-mm@kvack.org, rust-for-linux@vger.kernel.org, Alice Ryhl Content-Type: text/plain; charset="utf-8" X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: AA37714000C X-Stat-Signature: api8bossp1b1upikreu4m536ofu3twdu X-HE-Tag: 1741089110-161138 X-HE-Meta: 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 x3z0Cu7P 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.371311, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Adds an MmWithUserAsync type that uses mmput_async when dropped but is otherwise identical to MmWithUser. This has to be done using a separate type because the thing we are changing is the destructor. Rust Binder needs this to avoid a certain deadlock. See commit 9a9ab0d96362 ("binder: fix race between mmput() and do_exit()") for details. It's also needed in the shrinker to avoid cleaning up the mm in the shrinker's context. Acked-by: Lorenzo Stoakes Acked-by: Liam R. Howlett Reviewed-by: Andreas Hindborg Reviewed-by: Gary Guo Signed-off-by: Alice Ryhl --- rust/kernel/mm.rs | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) diff --git a/rust/kernel/mm.rs b/rust/kernel/mm.rs index 618aa48e00a442c7790dc92085932f5aa6693729..c7373d72bce558916f52fd62607b99025da8dbac 100644 --- a/rust/kernel/mm.rs +++ b/rust/kernel/mm.rs @@ -110,6 +110,50 @@ fn deref(&self) -> &Mm { } } +/// A wrapper for the kernel's `struct mm_struct`. +/// +/// This type is identical to `MmWithUser` except that it uses `mmput_async` when dropping a +/// refcount. This means that the destructor of `ARef` is safe to call in atomic +/// context. +/// +/// # Invariants +/// +/// Values of this type are always refcounted using `mmget`. The value of `mm_users` is non-zero. +#[repr(transparent)] +pub struct MmWithUserAsync { + mm: MmWithUser, +} + +// SAFETY: It is safe to call `mmput_async` on another thread than where `mmget` was called. +unsafe impl Send for MmWithUserAsync {} +// SAFETY: All methods on `MmWithUserAsync` can be called in parallel from several threads. +unsafe impl Sync for MmWithUserAsync {} + +// SAFETY: By the type invariants, this type is always refcounted. +unsafe impl AlwaysRefCounted for MmWithUserAsync { + #[inline] + fn inc_ref(&self) { + // SAFETY: The pointer is valid since self is a reference. + unsafe { bindings::mmget(self.as_raw()) }; + } + + #[inline] + unsafe fn dec_ref(obj: NonNull) { + // SAFETY: The caller is giving up their refcount. + unsafe { bindings::mmput_async(obj.cast().as_ptr()) }; + } +} + +// Make all `MmWithUser` methods available on `MmWithUserAsync`. +impl Deref for MmWithUserAsync { + type Target = MmWithUser; + + #[inline] + fn deref(&self) -> &MmWithUser { + &self.mm + } +} + // These methods are safe to call even if `mm_users` is zero. impl Mm { /// Returns a raw pointer to the inner `mm_struct`. @@ -161,6 +205,13 @@ pub unsafe fn from_raw<'a>(ptr: *const bindings::mm_struct) -> &'a MmWithUser { unsafe { &*ptr.cast() } } + /// Use `mmput_async` when dropping this refcount. + #[inline] + pub fn into_mmput_async(me: ARef) -> ARef { + // SAFETY: The layouts and invariants are compatible. + unsafe { ARef::from_raw(ARef::into_raw(me).cast()) } + } + /// Attempt to access a vma using the vma read lock. /// /// This is an optimistic trylock operation, so it may fail if there is contention. In that -- 2.48.1.711.g2feabab25a-goog