---
id: CVE-2025-38063
title: 'dm: fix unconditional IO throttle caused by REQ_PREFLUSH'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  dm: fix unconditional IO throttle caused by REQ_PREFLUSH

  When a bio with REQ_PREFLUSH is submitted to dm, __send_empty_flush()
  generates a flush_bio with REQ_OP_WRITE …
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= e34cbd307477ae07c5d8a8d0bd15e65a9ddaba5c <
    95d08924335f3b6f4ea0b92ebfe4fe0731c502d9
  - >-
    Linux >= e34cbd307477ae07c5d8a8d0bd15e65a9ddaba5c <
    52aa28f7b1708d76e315d78b5ed397932a1a97c3
  - >-
    Linux >= e34cbd307477ae07c5d8a8d0bd15e65a9ddaba5c <
    b55a97d1bd4083729a60d19beffe85d4c96680de
  - >-
    Linux >= e34cbd307477ae07c5d8a8d0bd15e65a9ddaba5c <
    2858cda9a8d95e6deee7e3b0a26adde696a9a4f5
  - >-
    Linux >= e34cbd307477ae07c5d8a8d0bd15e65a9ddaba5c <
    88f7f56d16f568f19e1a695af34a7f4a6ce537a6
  - Linux 4.10
published: '2025-06-18'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T01:06:24.829Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-38063'
references:
  - url: 'https://git.kernel.org/stable/c/95d08924335f3b6f4ea0b92ebfe4fe0731c502d9'
  - url: 'https://git.kernel.org/stable/c/52aa28f7b1708d76e315d78b5ed397932a1a97c3'
  - url: 'https://git.kernel.org/stable/c/b55a97d1bd4083729a60d19beffe85d4c96680de'
  - url: 'https://git.kernel.org/stable/c/2858cda9a8d95e6deee7e3b0a26adde696a9a4f5'
  - url: 'https://git.kernel.org/stable/c/88f7f56d16f568f19e1a695af34a7f4a6ce537a6'
tags:
  - cve.org
epss: 0.00182
epssPercentile: 0.07868
ingestedAt: '2026-10-15T05:52:46.098Z'
---

## Overview

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

dm: fix unconditional IO throttle caused by REQ_PREFLUSH

When a bio with REQ_PREFLUSH is submitted to dm, __send_empty_flush()
generates a flush_bio with REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC,
which causes the flush_bio to be throttled by wbt_wait().

An example from v5.4, similar problem also exists in upstream:

    crash> bt 2091206
    PID: 2091206  TASK: ffff2050df92a300  CPU: 109  COMMAND: "kworker/u260:0"
     #0 [ffff800084a2f7f0] __switch_to at ffff80004008aeb8
     #1 [ffff800084a2f820] __schedule at ffff800040bfa0c4
     #2 [ffff800084a2f880] schedule at ffff800040bfa4b4
     #3 [ffff800084a2f8a0] io_schedule at ffff800040bfa9c4
     #4 [ffff800084a2f8c0] rq_qos_wait at ffff8000405925bc
     #5 [ffff800084a2f940] wbt_wait at ffff8000405bb3a0
     #6 [ffff800084a2f9a0] __rq_qos_throttle at ffff800040592254
     #7 [ffff800084a2f9c0] blk_mq_make_request at ffff80004057cf38
     #8 [ffff800084a2fa60] generic_make_request at ffff800040570138
     #9 [ffff800084a2fae0] submit_bio at ffff8000405703b4
    #10 [ffff800084a2fb50] xlog_write_iclog at ffff800001280834 [xfs]
    #11 [ffff800084a2fbb0] xlog_sync at ffff800001280c3c [xfs]
    #12 [ffff800084a2fbf0] xlog_state_release_iclog at ffff800001280df4 [xfs]
    #13 [ffff800084a2fc10] xlog_write at ffff80000128203c [xfs]
    #14 [ffff800084a2fcd0] xlog_cil_push at ffff8000012846dc [xfs]
    #15 [ffff800084a2fda0] xlog_cil_push_work at ffff800001284a2c [xfs]
    #16 [ffff800084a2fdb0] process_one_work at ffff800040111d08
    #17 [ffff800084a2fe00] worker_thread at ffff8000401121cc
    #18 [ffff800084a2fe70] kthread at ffff800040118de4

After commit 2def2845cc33 ("xfs: don't allow log IO to be throttled"),
the metadata submitted by xlog_write_iclog() should not be throttled.
But due to the existence of the dm layer, throttling flush_bio indirectly
causes the metadata bio to be throttled.

Fix this by conditionally adding REQ_IDLE to flush_bio.bi_opf, which makes
wbt_should_throttle() return false to avoid wbt_wait().

## Affected

- `Linux >= e34cbd307477ae07c5d8a8d0bd15e65a9ddaba5c < 95d08924335f3b6f4ea0b92ebfe4fe0731c502d9`
- `Linux >= e34cbd307477ae07c5d8a8d0bd15e65a9ddaba5c < 52aa28f7b1708d76e315d78b5ed397932a1a97c3`
- `Linux >= e34cbd307477ae07c5d8a8d0bd15e65a9ddaba5c < b55a97d1bd4083729a60d19beffe85d4c96680de`
- `Linux >= e34cbd307477ae07c5d8a8d0bd15e65a9ddaba5c < 2858cda9a8d95e6deee7e3b0a26adde696a9a4f5`
- `Linux >= e34cbd307477ae07c5d8a8d0bd15e65a9ddaba5c < 88f7f56d16f568f19e1a695af34a7f4a6ce537a6`
- `Linux 4.10`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.