Subject: CVE-2022-48800: mm: vmscan: remove deadlock due to throttling failing to make progress

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

mm: vmscan: remove deadlock due to throttling failing to make progress

A soft lockup bug in kcompactd was reported in a private bugzilla with
the following visible in dmesg;

  watchdog: BUG: soft lockup - CPU#33 stuck for 26s! [kcompactd0:479]
  watchdog: BUG: soft lockup - CPU#33 stuck for 52s! [kcompactd0:479]
  watchdog: BUG: soft lockup - CPU#33 stuck for 78s! [kcompactd0:479]
  watchdog: BUG: soft lockup - CPU#33 stuck for 104s! [kcompactd0:479]

The machine had 256G of RAM with no swap and an earlier failed
allocation indicated that node 0 where kcompactd was run was potentially
unreclaimable;

  Node 0 active_anon:29355112kB inactive_anon:2913528kB active_file:0kB
    inactive_file:0kB unevictable:64kB isolated(anon):0kB isolated(file):0kB
    mapped:8kB dirty:0kB writeback:0kB shmem:26780kB shmem_thp:
    0kB shmem_pmdmapped: 0kB anon_thp: 23480320kB writeback_tmp:0kB
    kernel_stack:2272kB pagetables:24500kB all_unreclaimable? yes

Vlastimil Babka investigated a crash dump and found that a task
migrating pages was trying to drain PCP lists;

  PID: 52922  TASK: ffff969f820e5000  CPU: 19  COMMAND: "kworker/u128:3"
  Call Trace:
     __schedule
     schedule
     schedule_timeout
     wait_for_completion
     __flush_work
     __drain_all_pages
     __alloc_pages_slowpath.constprop.114
     __alloc_pages
     alloc_migration_target
     migrate_pages
     migrate_to_node
     do_migrate_pages
     cpuset_migrate_mm_workfn
     process_one_work
     worker_thread
     kthread
     ret_from_fork

This failure is specific to CONFIG_PREEMPT=n builds.  The root of the
problem is that kcompact0 is not rescheduling on a CPU while a task that
has isolated a large number of the pages from the LRU is waiting on
kcompact0 to reschedule so the pages can be released.  While
shrink_inactive_list() only loops once around too_many_isolated, reclaim
can continue without rescheduling if sc->skipped_deactivate == 1 which
could happen if there was no file LRU and the inactive anon list was not
low.

The Linux kernel CVE team has assigned CVE-2022-48800 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.16 with commit d818fca1cac3 and fixed in 5.16.10 with commit 3980cff63496
	Issue introduced in 5.16 with commit d818fca1cac3 and fixed in 5.17 with commit b485c6f1f9f5

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2022-48800
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	mm/vmscan.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/3980cff6349687f73d5109f156f23cb261c24164
	https://git.kernel.org/stable/c/b485c6f1f9f54b81443efda5f3d8a5036ba2cd91