Message-ID: <aIg87RSWc8-KbQ4v@ysun46-mobl.ccr.corp.intel.com>
Date: Tue, 29 Jul 2025 11:15:57 +0800
From: Yi Sun <yi.sun@...el.com>
To: Shuai Xue <xueshuai@...ux.alibaba.com>
CC: Fenghua Yu <fenghuay@...dia.com>, <vinicius.gomes@...el.com>,
	<dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<dave.jiang@...el.com>, <gordon.jin@...el.com>
Subject: Re: [PATCH v3 2/2] dmaengine: idxd: Fix refcount underflow on module
 unload

On 29.07.2025 10:46, Shuai Xue wrote:
>
>
>在 2025/7/28 19:43, Yi Sun 写道:
>>On 28.07.2025 16:40, Shuai Xue wrote:
>>>Hi, Yi Sun, Fenghua Yu,
>>>
>>>在 2025/7/27 17:16, Yi Sun 写道:
>>>>On 17.06.2025 14:58, Fenghua Yu wrote:
>>>>>Hi, Yi,
>>>>>
>>>>>On 6/17/25 03:27, Yi Sun wrote:
>>>>>>A recent refactor introduced a misplaced put_device() call, leading to a
>>>>>>reference count underflow during module unload.
>>>>>>
>>>>>>There is no need to add additional put_device() calls for idxd groups,
>>>>>>engines, or workqueues. Although commit a409e919ca3 claims:"Note, this
>>>>>>also fixes the missing put_device() for idxd groups, engines, and wqs."
>>>>>>It appears no such omission existed. The required cleanup is already
>>>>>>handled by the call chain:
>>>>>>
>>>>>>
>>>>>>Extend idxd_cleanup() to perform the necessary cleanup, and remove
>>>>>>idxd_cleanup_internals() which was not originally part of the driver
>>>>>>unload path and introduced unintended reference count underflow.
>>>>>>
>>>>>>Fixes: a409e919ca32 ("dmaengine: idxd: Refactor remove call with idxd_cleanup() helper")
>>>>>>Signed-off-by: Yi Sun <yi.sun@...el.com>
>>>>>>
>>>>>>diff --git a/drivers/dma/idxd/init.c b/drivers/dma/idxd/init.c
>>>>>>index 40cc9c070081..40f4bf446763 100644
>>>>>>--- a/drivers/dma/idxd/init.c
>>>>>>+++ b/drivers/dma/idxd/init.c
>>>>>>@@ -1292,7 +1292,10 @@ static void idxd_remove(struct pci_dev *pdev)
>>>>>>    device_unregister(idxd_confdev(idxd));
>>>>>>    idxd_shutdown(pdev);
>>>>>>    idxd_device_remove_debugfs(idxd);
>>>>>>-    idxd_cleanup(idxd);
>>>>>>+    perfmon_pmu_remove(idxd);
>>>>>>+    idxd_cleanup_interrupts(idxd);
>>>>>>+    if (device_pasid_enabled(idxd))
>>>>>>+        idxd_disable_system_pasid(idxd);
>>>>>>
>>>>>This will hit memory leak issue.
>>>>>
>>>>>idxd_remove_internals() does not only put_device() but also free allocated memory for wqs, engines, groups. Without calling idxd_remove_internals(), the allocated memory is leaked.
>>>>>
>>>>>I think a right fix is to remove the put_device() in idxd_cleanup_wqs/engines/groups() because:
>>>>>
>>>>>1. idxd_setup_wqs/engines/groups() does not call get_device(). Their counterpart idxd_cleanup_wqs/engines/groups() shouldn't call put_device().
>>>>>
>>>>>2. Fix the issue mentioned in this patch while there is no memory leak issue.
>>>>>
>>>>>>    pci_iounmap(pdev, idxd->reg_base);
>>>>>>    put_device(idxd_confdev(idxd));
>>>>>>    pci_disable_device(pdev);
>>>>>
>>>>>Thanks.
>>>>>
>>>>>-Fenghua
>>>>>
>>>>
>>>>Hi Fenghua,
>>>>
>>>>As with the comments on the previous patch, the function
>>>>idxd_conf_device_release already covers part of what is done in
>>>>idxd_remove_internals, including:
>>>>    kfree(idxd->groups);
>>>>    kfree(idxd->wqs);
>>>>    kfree(idxd->engines);
>>>>    kfree(idxd);
>>>>
>>>>We need to redesign idxd_remove_internals to clearly identify what
>>>>truely result in memory leaks and should be handled there.
>>>>Then, we'll need another patch to fix the idxd_remove_internals and call
>>>>it here.
>>>>
>>>>Let's prioritize addressing the two critical issues we've encountered here,
>>>>and then revisit the memory leak discussion afterward.
>>>>
>>>>Thanks
>>>>  --Sun, Yi
>>>
>>>The root cause is simliar to Patch 1, the idxd_conf_device_release()
>>>function already handles part of the cleanup that
>>>idxd_cleanup_internals() attempts to do, e.g.
>>>
>>>   idxd->wqs
>>>   idxd->einges
>>>   idxd->groups
>>>
>>>As a result, it causes user-after-free issue.
>>>
>>>   ------------[ cut here ]------------
>>>   WARNING: CPU: 190 PID: 13854 at lib/refcount.c:28 refcount_warn_saturate+0xbe/0x110
>>>   refcount_t: underflow; use-after-free.
>>>   drm_client_lib(E) i2c_algo_bit(E) drm_shmem_helper(E) drm_kms_helper(E) nvme(E) mlx5_core(E) mlxfw(E) nvme_core(E) pci_hyperv_intf(E) psample(E) drm(E) wmi(E) pinctrl_emmitsburg(E) sd_mod(E) sg(E) ahci(E) libahci(E) libata(E) fuse(E)
>>>   Modules linked in: binfmt_misc(E) bonding(E) tls(E) intel_rapl_msr(E) intel_rapl_common(E) intel_uncore_frequency(E) intel_uncore_frequency_common(E) i10nm_edac(E) skx_edac_common(E) nfit(E) x86_pkg_temp_thermal(E) intel_powerclamp(E) coretemp(E) kvm_intel(E) snd_hda_intel(E) kvm(E) snd_intel_dspcfg(E) snd_hda_codec(E) mlx5_ib(E) irqbypass(E) qat_4xxx(E) snd_hda_core(E) dax_hmem(E) ghash_clmulni_intel(E) intel_qat(E) cxl_acpi(E) snd_hwdep(E) rapl(E) snd_pcm(E) cxl_port(E) iTCO_wdt(E) intel_cstate(E) iTCO_vendor_support(E) snd_timer(E) ib_uverbs(E) pmt_telemetry(E) cxl_core(E) rfkill(E) tun(E) dh_generic(E) pmt_class(E) intel_uncore(E) einj(E) pcspkr(E) isst_if_mbox_pci(E) joydev(E) isst_if_mmio(E) idxd(E-) crc8(E) ib_core(E) isst_if_common(E) authenc(E) intel_vsec(E) idxd_bus(E) snd(E) i2c_i801(E) mei_me(E) soundcore(E) i2c_smbus(E) i2c_ismt(E) mei(E) nf_tables(E) nfnetlink(E) ipmi_ssif(E) acpi_power_meter(E) ipmi_si(E) acpi_ipmi(E) ipmi_devintf(E) ipmi_msghandle
>>>   CPU: 190 UID: 0 PID: 13854 Comm: rmmod Kdump: loaded Tainted: G S          E       6.16.0-rc6+ #116 PREEMPT(none)
>>>   Tainted: [S]=CPU_OUT_OF_SPEC, [E]=UNSIGNED_MODULE
>>>   Hardware name: Inspur AliServer-Xuanwu2.0-02-1UCG42PF/AS2111TG5, BIOS 3.0.ES.AL.P.090.01 02/22/2024
>>>   RIP: 0010:refcount_warn_saturate+0xbe/0x110
>>>   RSP: 0018:ff7078d2df957db8 EFLAGS: 00010282
>>>   RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
>>>   RBP: ff2b10355b055000 R08: 0000000000000000 R09: ff7078d2df957c68
>>>   RDX: ff2b10b33fdaa3c0 RSI: 0000000000000001 RDI: ff2b10b33fd9c440
>>>   R10: ff7078d2df957c60 R11: ffffffffbe761d68 R12: ff2b1035a00db400
>>>   R13: ff2b10355670b148 R14: ff2b103555097c80 R15: ffffffffc0a88938
>>>   FS:  00007fb5f8f3b740(0000) GS:ff2b10b380bb9000(0000) knlGS:0000000000000000
>>>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>   CR2: 00005560a898c2d8 CR3: 00000080f9def005 CR4: 0000000000f73ef0
>>>   PKRU: 55555554
>>>   Code: 01 01 e8 35 9b 9a ff 0f 0b c3 cc cc cc cc 80 3d 05 4c f5 01 00 75 85 48 c7 c7 30 21 75 bd c6 05 f5 4b f5 01 01 e8 12 9b 9a ff <0f> 0b c3 cc cc cc cc 80 3d e0 4b f5 01 00 0f 85 5e ff ff ff 48 c7
>>>   Call Trace:
>>>   idxd_cleanup+0x6b/0x100 [idxd]
>>>   <TASK>
>>>   idxd_remove+0x46/0x70 [idxd]
>>>   pci_device_remove+0x3f/0xb0
>>>   driver_detach+0x48/0x90
>>>   device_release_driver_internal+0x197/0x200
>>>   bus_remove_driver+0x6d/0xf0
>>>   idxd_exit_module+0x34/0x6c0 [idxd]
>>>   __do_sys_delete_module.constprop.0+0x174/0x310
>>>   do_syscall_64+0x5f/0x2d0
>>>   pci_unregister_driver+0x2e/0xb0
>>>   entry_SYSCALL_64_after_hwframe+0x76/0x7e
>>>   RIP: 0033:0x7fb5f8a620cb
>>>   Code: 73 01 c3 48 8b 0d a5 6d 19 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 b0 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 75 6d 19 00 f7 d8 64 89 01 48
>>>   RSP: 002b:00007ffeed6101c8 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0
>>>   RAX: ffffffffffffffda RBX: 00005560a8981790 RCX: 00007fb5f8a620cb
>>>   RDX: 000000000000000a RSI: 0000000000000800 RDI: 00005560a89817f8
>>>   R13: 00007ffeed612352 R14: 00005560a89812a0 R15: 00005560a8981790
>>>   R10: 00007fb5f8baaac0 R11: 0000000000000206 R12: 00007ffeed6103f0
>>>   </TASK>
>>>   ---[ end trace 0000000000000000 ]---
>>>
>>>With this patch applied, the user-after-free issue is fixed.
>>>
>>>But, there is still memory leaks in
>>>
>>>   idxd->wqs[i]
>>>   idxd->einges[i]
>>>   idxd->groups[i]
>>>
>>>I agree with Vinicius that we should cleanup in idxd_conf_device_release().
>>>
>>>Thanks.
>>>Shuai
>>
>>Appreciate Shuai's clarification. Yes, it would be better if fixing the memory
>>leak issue in idxd_conf_device_release() in a separate patch.
>>
>>@Shuai, please feel free to proceed if you'd like to cook a patch for it.
>>
>>Thanks
>>    --Sun, Yi
>
>Hi, Sun, Yi,
>
>I need to correct my previous analysis. After further investigation, I
>believe there is no memory leak in the current code. The device
>reference counting and memory management are properly handled through
>the Linux device model. Each component is freed at the conf_dev
>destruction time:
>
>
>    idxd->wqs[i] is freed by idxd_conf_wq_release()
>    idxd->einges[i] is freed by idxd_conf_engine_release()
>    idxd->groups[i] is freed by idxd_conf_group_release()
>
>
>Adding additional cleanup in idxd_conf_device_release() would actually
>cause double-free issues. I can reproduce this with KASAN:
>
>[kernel][err]BUG: KASAN: slab-use-after-free in idxd_clean_groups+0x137/0x250 [idxd]
>[kernel][err]==================================================================
>[kernel][err]Read of size 4 at addr ff1100822ff89038 by task rmmod/13956
>[kernel][err]
>[kernel][err]CPU: 185 UID: 0 PID: 13956 Comm: rmmod Kdump: loaded Tainted: G S          E       6.16.0-rc6+ #117 PREEMPT(none)
>[kernel][err]Tainted: [S]=CPU_OUT_OF_SPEC, [E]=UNSIGNED_MODULE
>[kernel][err]Hardware name: Inspur AliServer-Xuanwu2.0-02-1UCG42PF/AS2111TG5, BIOS 3.0.ES.AL.P.090.01 02/22/2024
>[kernel][err]Call Trace:
>[kernel][err]<TASK>
>[kernel][err]dump_stack_lvl+0x55/0x70
>[kernel][err]print_address_description.constprop.0+0x27/0x2e0
>[kernel][err]? idxd_clean_groups+0x137/0x250 [idxd]
>[kernel][err]print_report+0x3e/0x70
>[kernel][err]kasan_report+0xb8/0xf0
>[kernel][err]? idxd_clean_groups+0x137/0x250 [idxd]
>[kernel][err]kasan_check_range+0x39/0x1b0
>[kernel][err]idxd_clean_groups+0x137/0x250 [idxd]
>[kernel][err]idxd_cleanup_internals+0x1f/0x1b0 [idxd]
>[kernel][err]idxd_conf_device_release+0xe2/0x2b0 [idxd]
>[kernel][err]device_release+0x9c/0x210
>[kernel][err]kobject_cleanup+0x101/0x360
>[kernel][err]pci_device_remove+0xab/0x1e0
>[kernel][err]idxd_remove+0x93/0xb0 [idxd]
>[kernel][err]device_release_driver_internal+0x369/0x530
>[kernel][err]driver_detach+0xbf/0x180
>[kernel][err]bus_remove_driver+0x11b/0x2a0
>[kernel][err]pci_unregister_driver+0x2a/0x250
>[kernel][err]? kobject_put+0x55/0xe0
>[kernel][err]idxd_exit_module+0x34/0x40 [idxd]
>[kernel][err]__do_sys_delete_module.constprop.0+0x2ee/0x580
>[kernel][err]? fput_close_sync+0xdd/0x190
>[kernel][err]? __pfx___do_sys_delete_module.constprop.0+0x10/0x10
>[kernel][err]do_syscall_64+0x5d/0x2d0
>[kernel][err]? __pfx_fput_close_sync+0x10/0x10
>[kernel][err]entry_SYSCALL_64_after_hwframe+0x76/0x7e
>[kernel][err]RIP: 0033:0x7f2ac20620cb
>[kernel][err]Code: 73 01 c3 48 8b 0d a5 6d 19 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 b0 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 75 6d 19 00 f7 d8 64 89 01 48
>[kernel][err]RSP: 002b:00007ffdfec0a598 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0
>[kernel][err]RDX: 000000000000000a RSI: 0000000000000800 RDI: 0000560bd6bd77f8
>[kernel][err]RAX: ffffffffffffffda RBX: 0000560bd6bd7790 RCX: 00007f2ac20620cb
>[kernel][err]R10: 00007f2ac21aaac0 R11: 0000000000000206 R12: 00007ffdfec0a7c0
>[kernel][err]RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
>[kernel][err]</TASK>
>[kernel][err]R13: 00007ffdfec0b352 R14: 0000560bd6bd72a0 R15: 0000560bd6bd7790
>[kernel][err]Allocated by task 1445:
>[kernel][err]
>[kernel][warning]kasan_save_stack+0x24/0x50
>[kernel][warning]kasan_save_track+0x14/0x30
>[kernel][warning]__kasan_kmalloc+0xaa/0xb0
>[kernel][warning]idxd_setup_groups+0x2b5/0x7a0 [idxd]
>[kernel][warning]idxd_setup_internals+0xd1/0x6e0 [idxd]
>[kernel][warning]idxd_probe+0x93/0x310 [idxd]
>[kernel][warning]idxd_pci_probe_alloc+0x3f3/0x6e0 [idxd]
>[kernel][warning]local_pci_probe+0xe5/0x1a0
>[kernel][warning]work_for_cpu_fn+0x52/0xa0
>[kernel][warning]process_one_work+0x652/0x1080
>[kernel][warning]worker_thread+0x652/0xc70
>[kernel][warning]ret_from_fork+0x253/0x2e0
>[kernel][warning]kthread+0x34a/0x450
>[kernel][warning]ret_from_fork_asm+0x1a/0x30
>[kernel][err]
>[kernel][err]Freed by task 13956:
>[kernel][warning]kasan_save_stack+0x24/0x50
>[kernel][warning]kasan_save_track+0x14/0x30
>[kernel][warning]kasan_save_free_info+0x3a/0x60
>[kernel][warning]__kasan_slab_free+0x54/0x70
>[kernel][warning]kfree+0x12e/0x430
>[kernel][warning]device_release+0x9c/0x210
>[kernel][warning]kobject_cleanup+0x101/0x360
>[kernel][warning]idxd_unregister_devices+0x22d/0x320 [idxd]
>[kernel][warning]pci_device_remove+0xab/0x1e0
>[kernel][warning]idxd_remove+0x3c/0xb0 [idxd]
>[kernel][warning]driver_detach+0xbf/0x180
>[kernel][warning]device_release_driver_internal+0x369/0x530
>[kernel][warning]bus_remove_driver+0x11b/0x2a0
>[kernel][warning]pci_unregister_driver+0x2a/0x250
>[kernel][warning]idxd_exit_module+0x34/0x40 [idxd]
>[kernel][warning]do_syscall_64+0x5d/0x2d0
>[kernel][warning]__do_sys_delete_module.constprop.0+0x2ee/0x580
>[kernel][err]
>[kernel][err]The buggy address belongs to the object at ff1100822ff89000
>
>The issue shows memory being freed during device_release(), then
>accessed again in idxd_conf_device_release().
>
>Your original approach is correct - the kernel's device model handles
>the memory management properly, and we should not interfere with it.
>
>Feel free to add:
>
>Tested-by: Shuai Xue <xueshuai@...ux.alibaba.com>
>
>Sorry for the confusion in my earlier analysis.
>
>Best Regards,
>Shuai

I see. Thanks Shuai for the comments and testing efforts.
I'd like to resend this series with the Tested-by tag to make it easier
for further review.


Thanks
    --Sun, Yi

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