CVE-2024-57884: In the Linux kernel, the following vulnerability has been resolved:  mm: vmscan: account for free pages to prevent infinite Loop in throttle_direct_reclaim()  The task sometimes continues looping in throttle_direct_reclaim() because allow_direct_reclaim(pgdat) keeps returning false.     #0 [ffff80002cb6f8d0] __switch_to at ffff8000080095ac  #1 [ffff80002cb6f900] __schedule at ffff800008abbd1c  #2 [ffff80002cb6f990] schedule at ffff800008abc50c  #3 [ffff80002cb6f9b0] throttle_direct_reclaim at ffff800008273550  #4 [ffff80002cb6fa20] try_to_free_pages at ffff800008277b68  #5 [ffff80002cb6fae0] __alloc_pages_nodemask at ffff8000082c4660  #6 [ffff80002cb6fc50] alloc_pages_vma at ffff8000082e4a98  #7 [ffff80002cb6fca0] do_anonymous_page at ffff80000829f5a8  #8 [ffff80002cb6fce0] __handle_mm_fault at ffff8000082a5974  #9 [ffff80002cb6fd90] handle_mm_fault at ffff8000082a5bd4  At this point, the pgdat contains the following two zones:          NODE: 4  ZONE: 0  ADDR: ffff00817fffe540  NAME: "DMA32"           SIZE: 20480  MIN/LOW/HIGH: 11/28/45           VM_STAT:                 NR_FREE_PAGES: 359         NR_ZONE_INACTIVE_ANON: 18813           NR_ZONE_ACTIVE_ANON: 0         NR_ZONE_INACTIVE_FILE: 50           NR_ZONE_ACTIVE_FILE: 0           NR_ZONE_UNEVICTABLE: 0         NR_ZONE_WRITE_PENDING: 0                      NR_MLOCK: 0                     NR_BOUNCE: 0                    NR_ZSPAGES: 0             NR_FREE_CMA_PAGES: 0          NODE: 4  ZONE: 1  ADDR: ffff00817fffec00  NAME: "Normal"           SIZE: 8454144  PRESENT: 98304  MIN/LOW/HIGH: 68/166/264           VM_STAT:                 NR_FREE_PAGES: 146         NR_ZONE_INACTIVE_ANON: 94668           NR_ZONE_ACTIVE_ANON: 3         NR_ZONE_INACTIVE_FILE: 735           NR_ZONE_ACTIVE_FILE: 78           NR_ZONE_UNEVICTABLE: 0         NR_ZONE_WRITE_PENDING: 0                      NR_MLOCK: 0                     NR_BOUNCE: 0                    NR_ZSPAGES: 0             NR_FREE_CMA_PAGES: 0  In allow_direct_reclaim(), while processing ZONE_DMA32, the sum of inactive/active file-backed pages calculated in zone_reclaimable_pages() based on the result of zone_page_state_snapshot() is zero.    Additionally, since this system lacks swap, the calculation of inactive/ active anonymous pages is skipped.          crash> p nr_swap_pages         nr_swap_pages = $1937 = {           counter = 0         }  As a result, ZONE_DMA32 is deemed unreclaimable and skipped, moving on to the processing of the next zone, ZONE_NORMAL, despite ZONE_DMA32 having free pages significantly exceeding the high watermark.  The problem is that the pgdat->kswapd_failures hasn't been incremented.          crash> px ((struct pglist_data *) 0xffff00817fffe540)->kswapd_failures         $1935 = 0x0  This is because the node deemed balanced.  The node balancing logic in balance_pgdat() evaluates all zones collectively.  If one or more zones (e.g., ZONE_DMA32) have enough free pages to meet their watermarks, the entire node is deemed balanced.  This causes balance_pgdat() to exit early before incrementing the kswapd_failures, as it considers the overall memory state acceptable, even though some zones (like ZONE_NORMAL) remain under significant pressure.   The patch ensures that zone_reclaimable_pages() includes free pages (NR_FREE_PAGES) in its calculation when no other reclaimable pages are available (e.g., file-backed or anonymous pages).  This change prevents zones like ZONE_DMA32, which have sufficient free pages, from being mistakenly deemed unreclaimable.  By doing so, the patch ensures proper node balancing, avoids masking pressure on other zones like ZONE_NORMAL, and prevents infinite loops in throttle_direct_reclaim() caused by allow_direct_reclaim(pgdat) repeatedly returning false.   The kernel hangs due to a task stuck in throttle_direct_reclaim(), caused by a node being incorrectly deemed balanced despite pressure in certain zones, such as ZONE_NORMAL.  This issue arises from zone_reclaimable_pages ---truncated---