From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.15]) (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 3C3E334F486 for ; Tue, 17 Mar 2026 11:39:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.15 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773747602; cv=none; b=Gy3qOKcRm+8DhnPSdylbYNgNhUZYAhU7Xct4tNjkhlGCCZuv+XfbbWXgu70c7V95x/YNemaMQn11oidF12vqwrnXnKnJzx8sbyt4r6j5G/ApQkN5cigww0fOm7f9ZFFTZHS9CEE9YCU5okcPpF4mfHcOaRlALii6y0P05nEj1YA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773747602; c=relaxed/simple; bh=SRgtFoQIanVkXzBuwaf/6kB/9aC7bCosZ4GDzrkN5kQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=PssL6jpB+7RjN9Qizu+qjy965I0gv2CMIBS9186on8QYg7FjwgqVA3U/76zgUwEYIz0bedKtXTEctXBr91ydD6g9x8pYXF0zxI9oGVYT/pqgIGonV+w0ZCeOO7mj+JuS85eajUd3oR2ccszqO9Ec3d/B7HHPR+hTSgusXD5rBoQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=pass smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=JWM93Z7F; arc=none smtp.client-ip=192.198.163.15 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="JWM93Z7F" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1773747600; x=1805283600; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=SRgtFoQIanVkXzBuwaf/6kB/9aC7bCosZ4GDzrkN5kQ=; b=JWM93Z7FfXGNDuH2csdK+kBHvkoueZMmSgJyBTwNBZUMQSNt7fL3i8Iv slgpVTHm1U3+7yhWqylOI3z4+zK+Ui6Pqel4/hMU3DPU0KLARI3yWhWAX XKZj5z4D6jbV5dENFaQMtIGUW/NYs2ZLk7eo5h6HokBzSuEUW/UB4qzJ1 K1nUl4T+QgwrNrNOiX9nY3ox2wJ2F2sSJpvRfbVXf6859cE+MMPS26yQe IQf8fmun5pwX4IH8Mishw9OyK5Tp4vEH597LWCrYSGpUO9dD6N7OXAkag Wc8QPLWZIbysrA8rFELpv80a5k2ztTlRsmRYZLgNYXZUSRmtgSVVlaOjV g==; X-CSE-ConnectionGUID: vjRoCRmIQdytb/rN71Lo4A== X-CSE-MsgGUID: 2JPjt41aSmukTulPm9PppQ== X-IronPort-AV: E=McAfee;i="6800,10657,11731"; a="74893924" X-IronPort-AV: E=Sophos;i="6.23,124,1770624000"; d="scan'208";a="74893924" Received: from fmviesa005.fm.intel.com ([10.60.135.145]) by fmvoesa109.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Mar 2026 04:39:59 -0700 X-CSE-ConnectionGUID: xPRzCKTrSqOQHh5rh5AZ8w== X-CSE-MsgGUID: egKHkaI0QjGYmbobZe8KqQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,124,1770624000"; d="scan'208";a="226930061" Received: from dhhellew-desk2.ger.corp.intel.com (HELO fedora) ([10.245.245.163]) by fmviesa005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Mar 2026 04:39:56 -0700 From: =?UTF-8?q?Thomas=20Hellstr=C3=B6m?= To: stable@vger.kernel.org Cc: =?UTF-8?q?Thomas=20Hellstr=C3=B6m?= , Alistair Popple , Ralph Campbell , Christoph Hellwig , Jason Gunthorpe , Jason Gunthorpe , Leon Romanovsky , Andrew Morton , Matthew Brost , John Hubbard , linux-mm@kvack.org, dri-devel@lists.freedesktop.org, Rodrigo Vivi Subject: [PATCH 6.18.y] mm: Fix a hmm_range_fault() livelock / starvation problem Date: Tue, 17 Mar 2026 12:39:30 +0100 Message-ID: <20260317113930.193553-1-thomas.hellstrom@linux.intel.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026031727-elective-spilt-6870@gregkh> References: <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 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 (cherry picked from commit b570f37a2ce480be26c665345c5514686a8a0274) Signed-off-by: Thomas Hellström --- include/linux/migrate.h | 8 ++++++++ mm/filemap.c | 13 +++++++++---- mm/memory.c | 3 ++- 3 files changed, 19 insertions(+), 5 deletions(-) diff --git a/include/linux/migrate.h b/include/linux/migrate.h index 1f0ac122c3bf..8061efd89041 100644 --- a/include/linux/migrate.h +++ b/include/linux/migrate.h @@ -97,6 +97,14 @@ static inline int set_movable_ops(const struct movable_operations *ops, enum pag 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 diff --git a/mm/filemap.c b/mm/filemap.c index 024b71da5224..8a7f4ce69aff 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1386,14 +1386,16 @@ 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. + * 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_entry_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 61748b762876..e43f0a4702c4 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4642,7 +4642,8 @@ 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); + migration_entry_wait_on_locked(entry, vmf->ptl); } } else if (is_hwpoison_entry(entry)) { ret = VM_FAULT_HWPOISON; -- 2.53.0