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Message-ID: <b8d8cd51-41d4-4f8a-a885-baa41f5a587f@linux.alibaba.com>
Date: Mon, 28 Jul 2025 16:21:03 +0800
From: Shuai Xue <xueshuai@...ux.alibaba.com>
To: Yi Sun <yi.sun@...el.com>, Fenghua Yu <fenghuay@...dia.com>
Cc: 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 1/2] dmaengine: idxd: Remove improper idxd_free
Hi, Sun, Yi and Fenghua,
在 2025/7/27 17:02, Yi Sun 写道:
> On 17.06.2025 15:13, Fenghua Yu wrote:
>> Hi, Yi,
>>
>> On 6/17/25 03:27, Yi Sun wrote:
>>> The call to idxd_free() introduces a duplicate put_device() leading to a
>>> reference count underflow:
>>> refcount_t: underflow; use-after-free.
>>> WARNING: CPU: 15 PID: 4428 at lib/refcount.c:28 refcount_warn_saturate+0xbe/0x110
>>> ...
>>> Call Trace:
>>> <TASK>
>>> idxd_remove+0xe4/0x120 [idxd]
>>> pci_device_remove+0x3f/0xb0
>>> device_release_driver_internal+0x197/0x200
>>> driver_detach+0x48/0x90
>>> bus_remove_driver+0x74/0xf0
>>> pci_unregister_driver+0x2e/0xb0
>>> idxd_exit_module+0x34/0x7a0 [idxd]
>>> __do_sys_delete_module.constprop.0+0x183/0x280
>>> do_syscall_64+0x54/0xd70
>>> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>>>
>>> The idxd_unregister_devices() which is invoked at the very beginning of
>>> idxd_remove(), already takes care of the necessary put_device() through the
>>> following call path:
>>> idxd_unregister_devices() -> device_unregister() -> put_device()
>>>
>>> In addition, when CONFIG_DEBUG_KOBJECT_RELEASE is enabled, put_device() may
>>> trigger asynchronous cleanup via schedule_delayed_work(). If idxd_free() is
>>> called immediately after, it can result in a use-after-free.
>>>
>>> Remove the improper idxd_free() to avoid both the refcount underflow and
>>> potential memory corruption during module unload.
>>>
>>> Fixes: d5449ff1b04d ("dmaengine: idxd: Add missing idxd cleanup to fix memory leak in remove call")
>>> Signed-off-by: Yi Sun <yi.sun@...el.com>
>>>
>>> diff --git a/drivers/dma/idxd/init.c b/drivers/dma/idxd/init.c
>>> index 80355d03004d..40cc9c070081 100644
>>> --- a/drivers/dma/idxd/init.c
>>> +++ b/drivers/dma/idxd/init.c
>>> @@ -1295,7 +1295,6 @@ static void idxd_remove(struct pci_dev *pdev)
>>> idxd_cleanup(idxd);
>>> pci_iounmap(pdev, idxd->reg_base);
>>> put_device(idxd_confdev(idxd));
>>> - idxd_free(idxd);
>>
>> Simply removing idxd_free() causes two issues:
>>
>> 1. This hits memory leak issues because allocated idxd, ida, map are not freed.
>>
>> 2. There is still an underflow issue for dev refcnt in idxd_pci_probe_alloc() when idxd_register_devices() fails. Here get_device() is not called but put_device() is called.
>>
>> A right fix is to remove the put_device() in idxd_free(). This will fix all the above issues.
>>
>> Thanks.
>>
>> -Fenghua
>>
>
> Hi Fenghua,
> From my understanding, the function idxd_conf_device_release already
> covers everything done in idxd_free, including:
> bitmap_free(idxd->opcap_bmap);
> ida_free(&idxd_ida, idxd->id);
> kfree(idxd);
>
> At least the newly added idxd_free in commit 90022b3 doesn't resolve
> any memory leaks, but introduces several duplicated cleanup.
>
> reference:
> ```
> static void idxd_free(struct idxd_device *idxd)
> {
> if (!idxd)
> return;
>
> put_device(idxd_confdev(idxd));
> bitmap_free(idxd->opcap_bmap);
> ida_free(&idxd_ida, idxd->id);
> kfree(idxd);
> }
> ```
>
> V.S.
> ```
> static void idxd_conf_device_release(struct device *dev)
> {
> struct idxd_device *idxd = confdev_to_idxd(dev);
>
> kfree(idxd->groups);
> bitmap_free(idxd->wq_enable_map);
> kfree(idxd->wqs);
> kfree(idxd->engines);
> kfree(idxd->evl);
> kmem_cache_destroy(idxd->evl_cache);
> ida_free(&idxd_ida, idxd->id);
> bitmap_free(idxd->opcap_bmap);
> kfree(idxd);
> }
> ```
>
> Thanks
> --Sun, Yi
Thanks for the detailed analysis. After reviewing the code paths, I
agree with Yi Sun's assessment.
Looking at the call flow:
idxd_remove()
-> idxd_unregister_devices
-> idxd_conf_device_release
-> cleaup // first freed here
-> idxd_free
-> clean up // double freed here
The idxd_conf_device_release() function already handles all the cleanup
that idxd_free() attempts to do:
Calling idxd_free() after idxd_unregister_devices() results in
double-free issues. I can reproduce this with the following warning:
------------[ cut here ]------------
ida_free called for id=4 which is not allocated.
WARNING: CPU: 169 PID: 13495 at lib/idr.c:592 ida_free+0xe2/0x140
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) rfkill(E) kvm_intel(E) kvm(E) snd_hda_intel(E) snd_intel_dspcfg(E) snd_hda_codec(E) irqbypass(E) mlx5_ib(E) nf_tables(E) snd_hda_core(E) dax_hmem(E) ghash_clmulni_intel(E) snd_hwdep(E) cxl_acpi(E) rapl(E) snd_pcm(E) cxl_port(E) pmt_telemetry(E) iTCO_wdt(E) qat_4xxx(E) ib_uverbs(E) cxl_core(E) iTCO_vendor_support(E) pmt_class(E) isst_if_mbox_pci(E) intel_cstate(E) isst_if_mmio(E) snd_timer(E) tun(E) intel_qat(E) nfnetlink(E) intel_uncore(E) einj(E) pcspkr(E) joydev(E) ib_core(E) dh_generic(E) idxd(E-) crc8(E) isst_if_common(E) authenc(E) intel_vsec(E) idxd_bus(E) snd(E) mei_me(E) i2c_i801(E) soundcore(E) i2c_smbus(E) mei(E) i2c_ismt(E) ipmi_ssif(E) acpi_power_meter(E) ipmi_si(E) acpi_ipmi(E) ipmi_devintf(E) ipmi_msghandle
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)
CPU: 169 UID: 0 PID: 13495 Comm: rmmod Kdump: loaded Tainted: G S W E 6.16.0-rc6 #115 PREEMPT(none)
Tainted: [S]=CPU_OUT_OF_SPEC, [W]=WARN, [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:ida_free+0xe2/0x140
Code: f6 48 89 e7 e8 bf 2b 02 00 eb 5e 83 fb 3e 76 3a 48 8b 3c 24 4c 89 ee e8 bc a1 03 00 89 ee 48 c7 c7 b8 be 7a 9a e8 4e 70 2f ff <0f> 0b 48 8b 44 24 38 65 48 2b 05 17 11 20 02 75 3c 48 83 c4 40 5b
RSP: 0018:ff51ea5f331e3d78 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000004 RCX: ff3a3c153f85c448
RDX: 00000000ffffffd8 RSI: 0000000000000027 RDI: ff3a3c153f85c440
RBP: 0000000000000004 R08: 0000000000000000 R09: ff51ea5f331e3c28
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
R13: 0000000000000202 R14: ff3a3b97569ecc80 R15: ffffffffc0d41938
R10: ff51ea5f331e3c20 R11: ffffffff9b761d68 R12: 000000000000000f
FS: 00007f4c7e1c3740(0000) GS:ff3a3c15a3679000(0000) knlGS:0000000000000000
CR2: 0000562018b242c8 CR3: 00000080a849a004 CR4: 0000000000f73ef0
Call Trace:
<TASK>
PKRU: 55555554
idxd_remove+0x8d/0xa0 [idxd]
device_release_driver_internal+0x197/0x200
pci_device_remove+0x3f/0xb0
driver_detach+0x48/0x90
do_syscall_64+0x5f/0x2d0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
__do_sys_delete_module.constprop.0+0x174/0x310
idxd_exit_module+0x34/0x680 [idxd]
bus_remove_driver+0x6d/0xf0
pci_unregister_driver+0x2e/0xb0
RIP: 0033:0x7f4c7dc620cb
RSP: 002b:00007ffcb58d0b78 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0
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
RAX: ffffffffffffffda RBX: 0000562018b19780 RCX: 00007f4c7dc620cb
RDX: 000000000000000a RSI: 0000000000000800 RDI: 0000562018b197e8
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 00007f4c7ddaaac0 R11: 0000000000000206 R12: 00007ffcb58d0da0
</TASK>
R13: 00007ffcb58d2352 R14: 0000562018b192a0 R15: 0000562018b19780
Yi Sun's fix to remove the idxd_free() call is the correct approach. The
device release mechanism properly handles all the cleanup through the
established kernel device model.
Sorry for the confusion in the original implementation.
Tested-by: Shuai Xue <xueshuai@...ux.alibaba.com>
Best regards,
Shuai
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