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h=Subject:To:Cc:From:Date:From; b=PmxBHKrY9PX6Cvpr1C55nHd5fkGE18WYKIkiV2dC6Mob6NMwwPvFjbAc9rvCKMDfl ef4Y4Dy6dEgjaMsZ6jxKb23TxJE+BwGNwSVLXtSDtVoJ8ctsl0M9MxCAuEevsMx74O 2wTRrSJWu9MkzTYpHjfwCjWZvkYaiSfkQs8IIkvQ= Subject: Patch "mm: Fix a hmm_range_fault() livelock / starvation problem" has been added to the 6.18-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 16:38:58 +0100 Message-ID: <2026031757-jackknife-bacterium-3840@gregkh> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-stable: commit X-Patchwork-Hint: ignore X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: A2E2EA0013 X-Stat-Signature: yxwr77opra69td69dfrqhh4bwp5hfwxu X-HE-Tag: 1773762022-699618 X-HE-Meta: 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 ZPqOunKP 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 6.18-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-6.18 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: Thomas Hellström Signed-off-by: Greg Kroah-Hartman --- include/linux/migrate.h | 8 ++++++++ mm/filemap.c | 13 +++++++++---- mm/memory.c | 3 ++- 3 files changed, 19 insertions(+), 5 deletions(-) --- a/include/linux/migrate.h +++ b/include/linux/migrate.h @@ -97,6 +97,14 @@ static inline int set_movable_ops(const return -ENOSYS; } +static inline void migration_entry_wait_on_locked(swp_entry_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 @@ -1386,14 +1386,16 @@ repeat: #ifdef CONFIG_MIGRATION /** - * migration_entry_wait_on_locked - Wait for a migration entry to be removed - * @entry: migration swap entry. + * migration_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. @@ -1435,6 +1437,9 @@ void migration_entry_wait_on_locked(swp_ * 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 @@ -4642,7 +4642,8 @@ 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); + migration_entry_wait_on_locked(entry, vmf->ptl); } } else if (is_hwpoison_entry(entry)) { ret = VM_FAULT_HWPOISON; Patches currently in stable-queue which might be from thomas.hellstrom@linux.intel.com are queue-6.18/mm-fix-a-hmm_range_fault-livelock-starvation-problem.patch