Re: [PATCH] platform/x86: ISST: do not hold lock punit_misc_dev_lock when register misc

From: Hans de Goede
Date: Tue Jan 11 2022 - 05:39:26 EST

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In reply to: Liwei Song: "[PATCH] platform/x86: ISST: do not hold lock punit_misc_dev_lock when register misc"
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Hi,

On 1/11/22 11:31, Liwei Song wrote:
> exist the below call sequences may cause deadlock:
>
> isst_if_probe()
> --> isst_if_cdev_register()
> --> mutex_lock(&punit_misc_dev_lock)
> --> misc_register()
> --> mutex_lock(&misc_mtx)
>
> misc_open()
> --> mutex_lock(&misc_mtx)
> --> isst_if_open()
> --> mutex_lock(&punit_misc_dev_lock)
>
> to fix this do not hold punit_misc_dev_lock when call misc_register
> since it has misc_mtx lock for sync.

I agree that the punit_misc_dev_lock should not be hold during
(un)registration, but this fix looks wrong with unlocking + relocking it.

Normally things like this are done by setting up everything which needs
to be setup before calling misc_register() and in that case the
setup code does not need to lock the punit_misc_dev_lock at all since
none of the misc_dev callbacks can be called before everything is
setup (and the same in reverse for unregister, unregister the misc-dev
before doing any teardown, then there is no need for the lock).

Note the above assumes that the punit_misc_dev_lock is only used
from misc-dev callbacks based on its name, I did not check this is true.

Srinivas, can you take a look please ? And see if you can come up
with a better fix ?

Regards,

Hans

>
> [ 256.104522] ======================================================
> [ 256.113783] WARNING: possible circular locking dependency detected
> [ 256.120093] 5.16.0-rc6-yocto-standard+ #99 Not tainted
> [ 256.125362] ------------------------------------------------------
> [ 256.131673] intel-speed-sel/844 is trying to acquire lock:
> [ 256.137290] ffffffffc036f0d0 (punit_misc_dev_lock){+.+.}-{3:3}, at: isst_if_open+0x18/0x90 [isst_if_common]
> [ 256.147171]
> [ 256.147171] but task is already holding lock:
> [ 256.153135] ffffffff8ee7cb50 (misc_mtx){+.+.}-{3:3}, at: misc_open+0x2a/0x170
> [ 256.160407]
> [ 256.160407] which lock already depends on the new lock.
> [ 256.160407]
> [ 256.168712]
> [ 256.168712] the existing dependency chain (in reverse order) is:
> [ 256.176327]
> [ 256.176327] -> #1 (misc_mtx){+.+.}-{3:3}:
> [ 256.181946] lock_acquire+0x1e6/0x330
> [ 256.186265] __mutex_lock+0x9b/0x9b0
> [ 256.190497] mutex_lock_nested+0x1b/0x20
> [ 256.195075] misc_register+0x32/0x1a0
> [ 256.199390] isst_if_cdev_register+0x65/0x180 [isst_if_common]
> [ 256.205878] isst_if_probe+0x144/0x16e [isst_if_mmio]
> [ 256.209991] hrtimer: interrupt took 10370 ns
> [ 256.211582] local_pci_probe+0x47/0xa0
> [ 256.220384] work_for_cpu_fn+0x17/0x30
> [ 256.224790] process_one_work+0x26a/0x650
> [ 256.229456] worker_thread+0x1dd/0x3b0
> [ 256.233861] kthread+0x191/0x1c0
> [ 256.237745] ret_from_fork+0x1f/0x30
> [ 256.241976]
> [ 256.241976] -> #0 (punit_misc_dev_lock){+.+.}-{3:3}:
> [ 256.248552] validate_chain+0xbc6/0x1750
> [ 256.253131] __lock_acquire+0x88c/0xc10
> [ 256.257618] lock_acquire+0x1e6/0x330
> [ 256.261933] __mutex_lock+0x9b/0x9b0
> [ 256.266165] mutex_lock_nested+0x1b/0x20
> [ 256.270739] isst_if_open+0x18/0x90 [isst_if_common]
> [ 256.276356] misc_open+0x100/0x170
> [ 256.280409] chrdev_open+0xa5/0x1e0
> [ 256.284550] do_dentry_open+0x23d/0x3c0
> [ 256.289039] vfs_open+0x2f/0x40
> [ 256.292836] path_openat+0x87a/0x940
> [ 256.297064] do_filp_open+0xc5/0x140
> [ 256.301295] do_sys_openat2+0x23d/0x320
> [ 256.305782] do_sys_open+0x59/0x80
> [ 256.309836] __x64_sys_openat+0x20/0x30
> [ 256.314324] do_syscall_64+0x3f/0x90
> [ 256.318552] entry_SYSCALL_64_after_hwframe+0x44/0xae
> [ 256.324259]
> [ 256.324259] other info that might help us debug this:
> [ 256.324259]
> [ 256.332394] Possible unsafe locking scenario:
> [ 256.332394]
> [ 256.338444] CPU0 CPU1
> [ 256.343105] ---- ----
> [ 256.347768] lock(misc_mtx);
> [ 256.350870] lock(punit_misc_dev_lock);
> [ 256.357441] lock(misc_mtx);
> [ 256.363058] lock(punit_misc_dev_lock);
> [ 256.367110]
> [ 256.367110] *** DEADLOCK ***
> [ 256.367110]
> [ 256.373162] 1 lock held by intel-speed-sel/844:
> [ 256.377824] #0: ffffffff8ee7cb50 (misc_mtx){+.+.}-{3:3}, at: misc_open+0x2a/0x170
> [ 256.385531]
> [ 256.385531] stack backtrace:
> [ 256.390021] CPU: 12 PID: 844 Comm: intel-speed-sel Not tainted 5.16.0-rc6-yocto-standard+ #99
> [ 256.398678] Hardware name: ACCTON MOROCITY/MOROCITY, BIOS IDVLCRB1.86B.0021.D09.2111010103 11/01/2021
> [ 256.408028] Call Trace:
> [ 256.410605] <TASK>
> [ 256.412837] dump_stack_lvl+0x5b/0x82
> [ 256.416635] dump_stack+0x10/0x12
> [ 256.420085] print_circular_bug.isra.43+0x261/0x2c0
> [ 256.425095] check_noncircular+0x126/0x140
> [ 256.429326] ? __this_cpu_preempt_check+0x13/0x20
> [ 256.434167] validate_chain+0xbc6/0x1750
> [ 256.438223] ? validate_chain+0xbc6/0x1750
> [ 256.442451] ? validate_chain+0x236/0x1750
> [ 256.446687] __lock_acquire+0x88c/0xc10
> [ 256.450658] lock_acquire+0x1e6/0x330
> [ 256.454452] ? isst_if_open+0x18/0x90 [isst_if_common]
> [ 256.459726] ? __mutex_lock+0x79/0x9b0
> [ 256.463610] ? __mutex_lock+0x79/0x9b0
> [ 256.467493] ? isst_if_open+0x18/0x90 [isst_if_common]
> [ 256.472764] ? isst_if_open+0x18/0x90 [isst_if_common]
> [ 256.478038] __mutex_lock+0x9b/0x9b0
> [ 256.481748] ? isst_if_open+0x18/0x90 [isst_if_common]
> [ 256.487021] ? __mutex_lock+0x102/0x9b0
> [ 256.490993] ? __this_cpu_preempt_check+0x13/0x20
> [ 256.495837] mutex_lock_nested+0x1b/0x20
> [ 256.499893] ? mutex_lock_nested+0x1b/0x20
> [ 256.504121] isst_if_open+0x18/0x90 [isst_if_common]
> [ 256.509222] misc_open+0x100/0x170
> [ 256.512759] chrdev_open+0xa5/0x1e0
> [ 256.516386] ? cdev_put.part.1+0x20/0x20
> [ 256.520441] do_dentry_open+0x23d/0x3c0
> [ 256.524414] vfs_open+0x2f/0x40
> [ 256.527689] path_openat+0x87a/0x940
> [ 256.531399] do_filp_open+0xc5/0x140
> [ 256.535112] ? trace_preempt_on+0x28/0xd0
> [ 256.539255] ? alloc_fd+0x152/0x230
> [ 256.542880] ? preempt_count_sub+0x9b/0x100
> [ 256.547200] ? _raw_spin_unlock+0x2c/0x50
> [ 256.551348] do_sys_openat2+0x23d/0x320
> [ 256.555320] ? do_sys_openat2+0x23d/0x320
> [ 256.559467] do_sys_open+0x59/0x80
> [ 256.563003] __x64_sys_openat+0x20/0x30
> [ 256.566972] do_syscall_64+0x3f/0x90
> [ 256.570680] entry_SYSCALL_64_after_hwframe+0x44/0xae
> [ 256.575866] RIP: 0033:0x7f9be4b97c27
> [ 256.579576] Code: 25 00 00 41 00 3d 00 00 41 00 74 37 64 8b 04 25 18 00 00 00 85 c0 75 5b 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 0f 87 85 00 00 00 48 83 c4 68 5d 41 5c c3 0f 1f
> [ 256.598474] RSP: 002b:00007ffd8fc01b70 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
> [ 256.606177] RAX: ffffffffffffffda RBX: 00005572f20332b0 RCX: 00007f9be4b97c27
> [ 256.613443] RDX: 0000000000000000 RSI: 00005572f202936a RDI: 00000000ffffff9c
> [ 256.620709] RBP: 00005572f202936a R08: 0000000000000008 R09: 0000000000000001
> [ 256.627974] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> [ 256.635241] R13: 00005572f20332b0 R14: 0000000000000001 R15: 0000000000000000
> [ 256.642513] </TASK>
>
> Signed-off-by: Liwei Song <liwei.song@xxxxxxxxxxxxx>
> ---
> drivers/platform/x86/intel/speed_select_if/isst_if_common.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/platform/x86/intel/speed_select_if/isst_if_common.c b/drivers/platform/x86/intel/speed_select_if/isst_if_common.c
> index c9a85eb2e860..bcbc0d508ec4 100644
> --- a/drivers/platform/x86/intel/speed_select_if/isst_if_common.c
> +++ b/drivers/platform/x86/intel/speed_select_if/isst_if_common.c
> @@ -693,10 +693,12 @@ int isst_if_cdev_register(int device_type, struct isst_if_cmd_cb *cb)
> if (!misc_usage_count) {
> int ret;
>
> + mutex_unlock(&punit_misc_dev_lock);
> misc_device_ret = misc_register(&isst_if_char_driver);
> if (misc_device_ret)
> - goto unlock_exit;
> + return misc_device_ret;
>
> + mutex_lock(&punit_misc_dev_lock);
> ret = isst_if_cpu_info_init();
> if (ret) {
> misc_deregister(&isst_if_char_driver);
> @@ -731,7 +733,9 @@ void isst_if_cdev_unregister(int device_type)
> if (device_type == ISST_IF_DEV_MBOX)
> isst_delete_hash();
> if (!misc_usage_count && !misc_device_ret) {
> + mutex_unlock(&punit_misc_dev_lock);
> misc_deregister(&isst_if_char_driver);
> + mutex_lock(&punit_misc_dev_lock);
> isst_if_cpu_info_exit();
> }
> mutex_unlock(&punit_misc_dev_lock);
>

Next message: Michal Hocko: "Re: [PATCH v6 0/9] Multigenerational LRU Framework"
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In reply to: Liwei Song: "[PATCH] platform/x86: ISST: do not hold lock punit_misc_dev_lock when register misc"
Next in thread: Liwei Song: "Re: [PATCH] platform/x86: ISST: do not hold lock punit_misc_dev_lock when register misc"
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