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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 , linux-kernel@vger.kernel.org, linux-mm@kvack.org, rust-for-linux@vger.kernel.org, Alice Ryhl X-Rspamd-Queue-Id: 8A2E940014 X-Stat-Signature: wspu3d8iuicnhckhnreckcckkkjy5caq X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1739444689-650641 X-HE-Meta: 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 VorANykk 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 X-Bogosity: Unsure, tests=bogofilter, spamicity=0.458426, 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. Reviewed-by: Andreas Hindborg Acked-by: Lorenzo Stoakes (for mm bits) Signed-off-by: Alice Ryhl Reviewed-by: Gary Guo --- rust/kernel/mm.rs | 49 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) diff --git a/rust/kernel/mm.rs b/rust/kernel/mm.rs index 618aa48e00a4..42decd311740 100644 --- a/rust/kernel/mm.rs +++ b/rust/kernel/mm.rs @@ -110,6 +110,48 @@ 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 { + fn inc_ref(&self) { + // SAFETY: The pointer is valid since self is a reference. + unsafe { bindings::mmget(self.as_raw()) }; + } + + 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 +203,13 @@ 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