From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8FB23387353 for ; Tue, 17 Mar 2026 10:19:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773742773; cv=none; b=QzSu9+WMOzP8erzb4Imc1KhHCc1n+D80jlNnSYCW8XfEbHfViK8OOJ4APG6XQwKNXuy+YGn2QbvghigipDmof0J0hJtChiZzk/pQi+0ViWei2kRUB/TdL0Yf7lgePFtqsOSxm2LGvRP8IJXRtRdZjGm05c2+Jr4uvfwGYfSZFvs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773742773; c=relaxed/simple; bh=+UYckGZZN6NQTl2c2cTydojNQQNAcGEPsx+c2KwR6Bg=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=kPOAIFMngwcdHsJvNXsoULYnSBY/73E56KdONxU7dHHoWRl6VYkH+XDbu6Lb1Vg0tKUDt//0K1fWwFBmszizMobwAteZH/J7cnsgyU1+etLcaehP2DQDo7JkvoZZXr2v26LD/wpvDyVC7PvFUfu0rpwlNS+k/D4gJSXibNUQSCA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=L+a9A/1v; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="L+a9A/1v" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 573A2C4CEF7; Tue, 17 Mar 2026 10:19:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1773742773; bh=+UYckGZZN6NQTl2c2cTydojNQQNAcGEPsx+c2KwR6Bg=; h=Subject:To:Cc:From:Date:From; b=L+a9A/1vMNF+0hewIbC5FwIRVZSEJwyTV9tmrDbwdj0anC6t966wqIrlkGmfGNZo0 pLumgsO4AxzziUuEpaaiQWEzIP8+SZ6n5ITzNkcCs1NyZ4gJOCvf/dk0zmuawt0apI NMNVCrtum7ECl502xTSSgAfpItxlw76psPYy+qYE= Subject: FAILED: patch "[PATCH] mm: Fix a hmm_range_fault() livelock / starvation problem" failed to apply to 6.18-stable tree To: thomas.hellstrom@linux.intel.com,akpm@linux-foundation.org,apopple@nvidia.com,dri-devel@lists.freedesktop.org,hch@lst.de,jgg@mellanox.com,jgg@ziepe.ca,jhubbard@nvidia.com,leon@kernel.org,matthew.brost@intel.com,rcampbell@nvidia.com,rodrigo.vivi@intel.com,stable@vger.kernel.org Cc: From: Date: Tue, 17 Mar 2026 11:19:27 +0100 Message-ID: <2026031727-elective-spilt-6870@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.18-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y git checkout FETCH_HEAD git cherry-pick -x b570f37a2ce480be26c665345c5514686a8a0274 # git commit -s git send-email --to '' --in-reply-to '2026031727-elective-spilt-6870@gregkh' --subject-prefix 'PATCH 6.18.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >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: [PATCH] mm: Fix a hmm_range_fault() livelock / starvation problem MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 diff --git a/include/linux/migrate.h b/include/linux/migrate.h index 26ca00c325d9..d5af2b7f577b 100644 --- a/include/linux/migrate.h +++ b/include/linux/migrate.h @@ -65,7 +65,7 @@ bool isolate_folio_to_list(struct folio *folio, struct list_head *list); 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 struct movable_operations *ops, enum pag 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 diff --git a/mm/filemap.c b/mm/filemap.c index 6cd7974d4ada..406cef06b684 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1379,14 +1379,16 @@ static inline int folio_wait_bit_common(struct folio *folio, int bit_nr, #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 @@ static inline int folio_wait_bit_common(struct folio *folio, int bit_nr, * 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(softleaf_t entry, spinlock_t *ptl) * 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); diff --git a/mm/memory.c b/mm/memory.c index 07778814b4a8..2f815a34d924 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4763,7 +4763,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) 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; diff --git a/mm/migrate.c b/mm/migrate.c index 1bf2cf8c44dd..2c3d489ecf51 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -500,7 +500,7 @@ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd, 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); @@ -532,10 +532,10 @@ void migration_entry_wait_huge(struct vm_area_struct *vma, unsigned long addr, p * 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; } @@ -553,7 +553,7 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd) 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); diff --git a/mm/migrate_device.c b/mm/migrate_device.c index 0a8b31939640..8079676c8f1f 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -176,7 +176,7 @@ static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start, } if (softleaf_is_migration(entry)) { - migration_entry_wait_on_locked(entry, ptl); + softleaf_entry_wait_on_locked(entry, ptl); spin_unlock(ptl); return -EAGAIN; }