CVE-2026-64415: mm/swap: add cond_resched() in swap_reclaim_full_clusters to prevent softlockup

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

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

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

mm/swap: add cond_resched() in swap_reclaim_full_clusters to prevent softlockup

We hit a real softlockup in an internal stress test environment.  The
workload was LTP memory/swap stress on a large arm64 machine, with 320
CPUs, about 1TB memory and an 8.6GB swap device.  The system was under
heavy load and the swap device had a large number of full clusters.  The
softlockup was triggered during a stress test after about 3 days.

So, add periodic cond_resched() calls during large full_clusters
reclaim operations to prevent softlockup issues.

Detailed call trace as follow:

PID: 3817773  TASK: ffff0883bb28b780  CPU: 48   COMMAND: "kworker/48:7"
   #0 [ffff800080183d10] __crash_kexec at ffffa4c1361e5de4
   #1 [ffff800080183d90] panic at ffffa4c1360d5e9c
   #2 [ffff800080183e20] watchdog_timer_fn at ffffa4c136231fa8
   ...
  #16 [ffff8000c4ad3cb0] swap_cache_del_folio at ffffa4c1363e1614
  #17 [ffff8000c4ad3ce0] __try_to_reclaim_swap at ffffa4c1363e4bfc
  #18 [ffff8000c4ad3d40] swap_reclaim_full_clusters at ffffa4c1363e5474
  #19 [ffff8000c4ad3da0] swap_reclaim_work at ffffa4c1363e550c
  #20 [ffff8000c4ad3dc0] process_one_work at ffffa4c136102edc
  #21 [ffff8000c4ad3e10] worker_thread at ffffa4c136103398
  #22 [ffff8000c4ad3e70] kthread at ffffa4c13610d95c

The Linux kernel CVE team has assigned CVE-2026-64415 to this issue.


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

	Issue introduced in 6.12 with commit 5168a68eb78fa1c67a8b2d31d0642c7fd866cc12 and fixed in 6.12.96 with commit 60cbe67d1342f34b66df1c2ee328e3cd333767d7
	Issue introduced in 6.12 with commit 5168a68eb78fa1c67a8b2d31d0642c7fd866cc12 and fixed in 6.18.39 with commit 69c0e6246575b780ae0d3f411c749bcf13c221f3
	Issue introduced in 6.12 with commit 5168a68eb78fa1c67a8b2d31d0642c7fd866cc12 and fixed in 7.1.4 with commit 2a55fdf9f746a1a6ced7fd62ea1080b8a917e0b0
	Issue introduced in 6.12 with commit 5168a68eb78fa1c67a8b2d31d0642c7fd866cc12 and fixed in 7.2-rc1 with commit 66366d291f666ddeda5f8c84f253e308de3e6b55

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-2026-64415
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/swapfile.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/60cbe67d1342f34b66df1c2ee328e3cd333767d7
	https://git.kernel.org/stable/c/69c0e6246575b780ae0d3f411c749bcf13c221f3
	https://git.kernel.org/stable/c/2a55fdf9f746a1a6ced7fd62ea1080b8a917e0b0
	https://git.kernel.org/stable/c/66366d291f666ddeda5f8c84f253e308de3e6b55