From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1D2B1FD8741 for ; Tue, 17 Mar 2026 11:24:57 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 8332A10E5D0; Tue, 17 Mar 2026 11:24:56 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="xJaw0TnE"; dkim-atps=neutral Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id D459310E5D0 for ; Tue, 17 Mar 2026 11:24:54 +0000 (UTC) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 758AC41737; Tue, 17 Mar 2026 11:24:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DD75FC2BC9E; Tue, 17 Mar 2026 11:24:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1773746694; bh=0+/PiWhH1H9yOROoWEdYq9+vELjnzpbqXmH3HFEqGxI=; h=Subject:To:Cc:From:Date:From; b=xJaw0TnEB1DgtOGthTcKFTZfomtzyMeRbbatBtCVrHjvidkNAODgriaZM7NCqyYqS TL8Pqh8OscZ6sl+ht/83DVhlLbQ0IEZMmaN8d81tmz7jMbV2fIKu/mNTx8rvKeAal9 GDo57MAc6BeXa/NCmA9PyxHlqCuvnJl3vxGS0woI= Subject: Patch "mm: Fix a hmm_range_fault() livelock / starvation problem" has been added to the 6.19-stable tree To: akpm@linux-foundation.org, apopple@nvidia.com, dri-devel@lists.freedesktop.org, gregkh@linuxfoundation.org, hch@lst.de, jgg@mellanox.com, jgg@ziepe.ca, jhubbard@nvidia.com, leon@kernel.org, linux-mm@kvack.org, matthew.brost@intel.com, rcampbell@nvidia.com, rodrigo.vivi@intel.com, thomas.hellstrom@linux.intel.com Cc: From: Date: Tue, 17 Mar 2026 12:24:39 +0100 Message-ID: <2026031739-lusty-italicize-e41e@gregkh> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-stable: commit X-Patchwork-Hint: ignore X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" This is a note to let you know that I've just added the patch titled mm: Fix a hmm_range_fault() livelock / starvation problem to the 6.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: mm-fix-a-hmm_range_fault-livelock-starvation-problem.patch and it can be found in the queue-6.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >From b570f37a2ce480be26c665345c5514686a8a0274 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Thomas=20Hellstr=C3=B6m?= Date: Tue, 10 Feb 2026 12:56:53 +0100 Subject: mm: Fix a hmm_range_fault() livelock / starvation problem MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Thomas Hellström commit b570f37a2ce480be26c665345c5514686a8a0274 upstream. If hmm_range_fault() fails a folio_trylock() in do_swap_page, trying to acquire the lock of a device-private folio for migration, to ram, the function will spin until it succeeds grabbing the lock. However, if the process holding the lock is depending on a work item to be completed, which is scheduled on the same CPU as the spinning hmm_range_fault(), that work item might be starved and we end up in a livelock / starvation situation which is never resolved. This can happen, for example if the process holding the device-private folio lock is stuck in migrate_device_unmap()->lru_add_drain_all() sinc lru_add_drain_all() requires a short work-item to be run on all online cpus to complete. A prerequisite for this to happen is: a) Both zone device and system memory folios are considered in migrate_device_unmap(), so that there is a reason to call lru_add_drain_all() for a system memory folio while a folio lock is held on a zone device folio. b) The zone device folio has an initial mapcount > 1 which causes at least one migration PTE entry insertion to be deferred to try_to_migrate(), which can happen after the call to lru_add_drain_all(). c) No or voluntary only preemption. This all seems pretty unlikely to happen, but indeed is hit by the "xe_exec_system_allocator" igt test. Resolve this by waiting for the folio to be unlocked if the folio_trylock() fails in do_swap_page(). Rename migration_entry_wait_on_locked() to softleaf_entry_wait_unlock() and update its documentation to indicate the new use-case. Future code improvements might consider moving the lru_add_drain_all() call in migrate_device_unmap() to be called *after* all pages have migration entries inserted. That would eliminate also b) above. v2: - Instead of a cond_resched() in hmm_range_fault(), eliminate the problem by waiting for the folio to be unlocked in do_swap_page() (Alistair Popple, Andrew Morton) v3: - Add a stub migration_entry_wait_on_locked() for the !CONFIG_MIGRATION case. (Kernel Test Robot) v4: - Rename migrate_entry_wait_on_locked() to softleaf_entry_wait_on_locked() and update docs (Alistair Popple) v5: - Add a WARN_ON_ONCE() for the !CONFIG_MIGRATION version of softleaf_entry_wait_on_locked(). - Modify wording around function names in the commit message (Andrew Morton) Suggested-by: Alistair Popple Fixes: 1afaeb8293c9 ("mm/migrate: Trylock device page in do_swap_page") Cc: Ralph Campbell Cc: Christoph Hellwig Cc: Jason Gunthorpe Cc: Jason Gunthorpe Cc: Leon Romanovsky Cc: Andrew Morton Cc: Matthew Brost Cc: John Hubbard Cc: Alistair Popple Cc: linux-mm@kvack.org Cc: Signed-off-by: Thomas Hellström Cc: # v6.15+ Reviewed-by: John Hubbard #v3 Reviewed-by: Alistair Popple Link: https://patch.msgid.link/20260210115653.92413-1-thomas.hellstrom@linux.intel.com (cherry picked from commit a69d1ab971a624c6f112cea61536569d579c3215) Signed-off-by: Rodrigo Vivi Signed-off-by: Greg Kroah-Hartman --- include/linux/migrate.h | 10 +++++++++- mm/filemap.c | 15 ++++++++++----- mm/memory.c | 3 ++- mm/migrate.c | 8 ++++---- mm/migrate_device.c | 2 +- 5 files changed, 26 insertions(+), 12 deletions(-) --- a/include/linux/migrate.h +++ b/include/linux/migrate.h @@ -65,7 +65,7 @@ bool isolate_folio_to_list(struct folio int migrate_huge_page_move_mapping(struct address_space *mapping, struct folio *dst, struct folio *src); -void migration_entry_wait_on_locked(softleaf_t entry, spinlock_t *ptl) +void softleaf_entry_wait_on_locked(softleaf_t entry, spinlock_t *ptl) __releases(ptl); void folio_migrate_flags(struct folio *newfolio, struct folio *folio); int folio_migrate_mapping(struct address_space *mapping, @@ -97,6 +97,14 @@ static inline int set_movable_ops(const return -ENOSYS; } +static inline void softleaf_entry_wait_on_locked(softleaf_t entry, spinlock_t *ptl) + __releases(ptl) +{ + WARN_ON_ONCE(1); + + spin_unlock(ptl); +} + #endif /* CONFIG_MIGRATION */ #ifdef CONFIG_NUMA_BALANCING --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1379,14 +1379,16 @@ repeat: #ifdef CONFIG_MIGRATION /** - * migration_entry_wait_on_locked - Wait for a migration entry to be removed - * @entry: migration swap entry. + * softleaf_entry_wait_on_locked - Wait for a migration entry or + * device_private entry to be removed. + * @entry: migration or device_private swap entry. * @ptl: already locked ptl. This function will drop the lock. * - * Wait for a migration entry referencing the given page to be removed. This is + * Wait for a migration entry referencing the given page, or device_private + * entry referencing a dvice_private page to be unlocked. This is * equivalent to folio_put_wait_locked(folio, TASK_UNINTERRUPTIBLE) except * this can be called without taking a reference on the page. Instead this - * should be called while holding the ptl for the migration entry referencing + * should be called while holding the ptl for @entry referencing * the page. * * Returns after unlocking the ptl. @@ -1394,7 +1396,7 @@ repeat: * This follows the same logic as folio_wait_bit_common() so see the comments * there. */ -void migration_entry_wait_on_locked(softleaf_t entry, spinlock_t *ptl) +void softleaf_entry_wait_on_locked(softleaf_t entry, spinlock_t *ptl) __releases(ptl) { struct wait_page_queue wait_page; @@ -1428,6 +1430,9 @@ void migration_entry_wait_on_locked(soft * If a migration entry exists for the page the migration path must hold * a valid reference to the page, and it must take the ptl to remove the * migration entry. So the page is valid until the ptl is dropped. + * Similarly any path attempting to drop the last reference to a + * device-private page needs to grab the ptl to remove the device-private + * entry. */ spin_unlock(ptl); --- a/mm/memory.c +++ b/mm/memory.c @@ -4684,7 +4684,8 @@ vm_fault_t do_swap_page(struct vm_fault unlock_page(vmf->page); put_page(vmf->page); } else { - pte_unmap_unlock(vmf->pte, vmf->ptl); + pte_unmap(vmf->pte); + softleaf_entry_wait_on_locked(entry, vmf->ptl); } } else if (softleaf_is_hwpoison(entry)) { ret = VM_FAULT_HWPOISON; --- a/mm/migrate.c +++ b/mm/migrate.c @@ -499,7 +499,7 @@ void migration_entry_wait(struct mm_stru if (!softleaf_is_migration(entry)) goto out; - migration_entry_wait_on_locked(entry, ptl); + softleaf_entry_wait_on_locked(entry, ptl); return; out: spin_unlock(ptl); @@ -531,10 +531,10 @@ void migration_entry_wait_huge(struct vm * If migration entry existed, safe to release vma lock * here because the pgtable page won't be freed without the * pgtable lock released. See comment right above pgtable - * lock release in migration_entry_wait_on_locked(). + * lock release in softleaf_entry_wait_on_locked(). */ hugetlb_vma_unlock_read(vma); - migration_entry_wait_on_locked(entry, ptl); + softleaf_entry_wait_on_locked(entry, ptl); return; } @@ -552,7 +552,7 @@ void pmd_migration_entry_wait(struct mm_ ptl = pmd_lock(mm, pmd); if (!pmd_is_migration_entry(*pmd)) goto unlock; - migration_entry_wait_on_locked(softleaf_from_pmd(*pmd), ptl); + softleaf_entry_wait_on_locked(softleaf_from_pmd(*pmd), ptl); return; unlock: spin_unlock(ptl); --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -176,7 +176,7 @@ static int migrate_vma_collect_huge_pmd( } if (softleaf_is_migration(entry)) { - migration_entry_wait_on_locked(entry, ptl); + softleaf_entry_wait_on_locked(entry, ptl); spin_unlock(ptl); return -EAGAIN; } Patches currently in stable-queue which might be from thomas.hellstrom@linux.intel.com are queue-6.19/mm-fix-a-hmm_range_fault-livelock-starvation-problem.patch