CVE-2026-90183: blk-iolatency: clear delay state when freeing policy data

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

blk-iolatency: clear delay state when freeing policy data

io.latency can throttle a group which has no latency target of its own.
When a sibling misses its target, check_scale_change() scales down its
peers, and a peer that reaches queue depth one gets blkcg_use_delay()
called on it on every further scale-down, even with min_lat_nsec == 0.

iolatency_pd_offline() resets the target through
iolatency_set_min_lat_nsec(), which clears the delay only on a nonzero
to zero transition, so it never clears such a peer.  Freeing the policy
data then leaves blkg->use_delay set and blkcg->congestion_count
elevated with nothing left that can drop it.

blk_cgroup_congested() then returns true for every task in that cgroup
and its descendants for as long as the cgroup lives: page_cache_sync_ra()
cuts readahead to a single page, page_cache_async_ra() skips it
altogether, and __folio_throttle_swaprate() takes swap_avail_lock and
schedules a throttle on anonymous folio allocation.

Clear the delay in iolatency_pd_free().  By then bio-held blkg
references have drained, or the queue is frozen for policy
deactivation, so check_scale_change() cannot re-arm it.  The free
callback can also see policy data which was never attached to a blkg,
hence the pd->blkg check.

The Linux kernel CVE team has assigned CVE-2026-90183 to this issue.


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

	Issue introduced in 4.19 with commit d70675121546c35feaceebf7ed9caed8716640f3 and fixed in 7.2.6 with commit 02f1b90ab33ef99c89dd96a385b432ff57abc64d
	Issue introduced in 4.19 with commit d70675121546c35feaceebf7ed9caed8716640f3 and fixed in 7.3-rc1 with commit 8935bf22c0a0db517a7f72f7097300e05dd852f5

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-2026-90183
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:
	block/blk-iolatency.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/02f1b90ab33ef99c89dd96a385b432ff57abc64d
	https://git.kernel.org/stable/c/8935bf22c0a0db517a7f72f7097300e05dd852f5