CVE-2025-38063

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> dm: fix unconditional IO throttle caused by REQ_PREFLUSH<br /> <br /> When a bio with REQ_PREFLUSH is submitted to dm, __send_empty_flush()<br /> generates a flush_bio with REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC,<br /> which causes the flush_bio to be throttled by wbt_wait().<br /> <br /> An example from v5.4, similar problem also exists in upstream:<br /> <br /> crash&gt; bt 2091206<br /> PID: 2091206 TASK: ffff2050df92a300 CPU: 109 COMMAND: "kworker/u260:0"<br /> #0 [ffff800084a2f7f0] __switch_to at ffff80004008aeb8<br /> #1 [ffff800084a2f820] __schedule at ffff800040bfa0c4<br /> #2 [ffff800084a2f880] schedule at ffff800040bfa4b4<br /> #3 [ffff800084a2f8a0] io_schedule at ffff800040bfa9c4<br /> #4 [ffff800084a2f8c0] rq_qos_wait at ffff8000405925bc<br /> #5 [ffff800084a2f940] wbt_wait at ffff8000405bb3a0<br /> #6 [ffff800084a2f9a0] __rq_qos_throttle at ffff800040592254<br /> #7 [ffff800084a2f9c0] blk_mq_make_request at ffff80004057cf38<br /> #8 [ffff800084a2fa60] generic_make_request at ffff800040570138<br /> #9 [ffff800084a2fae0] submit_bio at ffff8000405703b4<br /> #10 [ffff800084a2fb50] xlog_write_iclog at ffff800001280834 [xfs]<br /> #11 [ffff800084a2fbb0] xlog_sync at ffff800001280c3c [xfs]<br /> #12 [ffff800084a2fbf0] xlog_state_release_iclog at ffff800001280df4 [xfs]<br /> #13 [ffff800084a2fc10] xlog_write at ffff80000128203c [xfs]<br /> #14 [ffff800084a2fcd0] xlog_cil_push at ffff8000012846dc [xfs]<br /> #15 [ffff800084a2fda0] xlog_cil_push_work at ffff800001284a2c [xfs]<br /> #16 [ffff800084a2fdb0] process_one_work at ffff800040111d08<br /> #17 [ffff800084a2fe00] worker_thread at ffff8000401121cc<br /> #18 [ffff800084a2fe70] kthread at ffff800040118de4<br /> <br /> After commit 2def2845cc33 ("xfs: don&amp;#39;t allow log IO to be throttled"),<br /> the metadata submitted by xlog_write_iclog() should not be throttled.<br /> But due to the existence of the dm layer, throttling flush_bio indirectly<br /> causes the metadata bio to be throttled.<br /> <br /> Fix this by conditionally adding REQ_IDLE to flush_bio.bi_opf, which makes<br /> wbt_should_throttle() return false to avoid wbt_wait().