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devcoredump: Fix circular locking dependency with devcd->mutex.

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The original code causes a circular locking dependency found by lockdep.

======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc6-lgci-xe-xe-pw-151626v3+ #1 Tainted: G S   U
------------------------------------------------------
xe_fault_inject/5091 is trying to acquire lock:
ffff888156815688 ((work_completion)(&(&devcd->del_wk)->work)){+.+.}-{0:0}, at: __flush_work+0x25d/0x660

but task is already holding lock:

ffff888156815620 (&devcd->mutex){+.+.}-{3:3}, at: dev_coredump_put+0x3f/0xa0
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&devcd->mutex){+.+.}-{3:3}:
       mutex_lock_nested+0x4e/0xc0
       devcd_data_write+0x27/0x90
       sysfs_kf_bin_write+0x80/0xf0
       kernfs_fop_write_iter+0x169/0x220
       vfs_write+0x293/0x560
       ksys_write+0x72/0xf0
       __x64_sys_write+0x19/0x30
       x64_sys_call+0x2bf/0x2660
       do_syscall_64+0x93/0xb60
       entry_SYSCALL_64_after_hwframe+0x76/0x7e
-> #1 (kn->active#236){++++}-{0:0}:
       kernfs_drain+0x1e2/0x200
       __kernfs_remove+0xae/0x400
       kernfs_remove_by_name_ns+0x5d/0xc0
       remove_files+0x54/0x70
       sysfs_remove_group+0x3d/0xa0
       sysfs_remove_groups+0x2e/0x60
       device_remove_attrs+0xc7/0x100
       device_del+0x15d/0x3b0
       devcd_del+0x19/0x30
       process_one_work+0x22b/0x6f0
       worker_thread+0x1e8/0x3d0
       kthread+0x11c/0x250
       ret_from_fork+0x26c/0x2e0
       ret_from_fork_asm+0x1a/0x30
-> #0 ((work_completion)(&(&devcd->del_wk)->work)){+.+.}-{0:0}:
       __lock_acquire+0x1661/0x2860
       lock_acquire+0xc4/0x2f0
       __flush_work+0x27a/0x660
       flush_delayed_work+0x5d/0xa0
       dev_coredump_put+0x63/0xa0
       xe_driver_devcoredump_fini+0x12/0x20 [xe]
       devm_action_release+0x12/0x30
       release_nodes+0x3a/0x120
       devres_release_all+0x8a/0xd0
       device_unbind_cleanup+0x12/0x80
       device_release_driver_internal+0x23a/0x280
       device_driver_detach+0x14/0x20
       unbind_store+0xaf/0xc0
       drv_attr_store+0x21/0x50
       sysfs_kf_write+0x4a/0x80
       kernfs_fop_write_iter+0x169/0x220
       vfs_write+0x293/0x560
       ksys_write+0x72/0xf0
       __x64_sys_write+0x19/0x30
       x64_sys_call+0x2bf/0x2660
       do_syscall_64+0x93/0xb60
       entry_SYSCALL_64_after_hwframe+0x76/0x7e
other info that might help us debug this:
Chain exists of: (work_completion)(&(&devcd->del_wk)->work) --> kn->active#236 --> &devcd->mutex
 Possible unsafe locking scenario:
       CPU0                    CPU1
       ----                    ----
  lock(&devcd->mutex);
                               lock(kn->active#236);
                               lock(&devcd->mutex);
  lock((work_completion)(&(&devcd->del_wk)->work));
 *** DEADLOCK ***
5 locks held by xe_fault_inject/5091:
 #0: ffff8881129f9488 (sb_writers#5){.+.+}-{0:0}, at: ksys_write+0x72/0xf0
 #1: ffff88810c755078 (&of->mutex#2){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x123/0x220
 #2: ffff8881054811a0 (&dev->mutex){....}-{3:3}, at: device_release_driver_internal+0x55/0x280
 #3: ffff888156815620 (&devcd->mutex){+.+.}-{3:3}, at: dev_coredump_put+0x3f/0xa0
 #4: ffffffff8359e020 (rcu_read_lock){....}-{1:2}, at: __flush_work+0x72/0x660
stack backtrace:
CPU: 14 UID: 0 PID: 5091 Comm: xe_fault_inject Tainted: G S   U              6.16.0-rc6-lgci-xe-xe-pw-151626v3+ #1 PREEMPT_{RT,(lazy)}
Tainted: [S]=CPU_OUT_OF_SPEC, [U]=USER
Hardware name: Micro-Star International Co., Ltd. MS-7D25/PRO Z690-A DDR4(MS-7D25), BIOS 1.10 12/13/2021
Call Trace:
 <TASK>
 dump_stack_lvl+0x91/0xf0
 dump_stack+0x10/0x20
 print_circular_bug+0x285/0x360
 check_noncircular+0x135/0x150
 ? register_lock_class+0x48/0x4a0
 __lock_acquire+0x1661/0x2860
 lock_acquire+0xc4/0x2f0
 ? __flush_work+0x25d/0x660
 ? mark_held_locks+0x46/0x90
 ? __flush_work+0x25d/0x660
 __flush_work+0x27a/0x660
 ? __flush_work+0x25d/0x660
 ? trace_hardirqs_on+0x1e/0xd0
 ? __pfx_wq_barrier_func+0x10/0x10
 flush_delayed_work+0x5d/0xa0
 dev_coredump_put+0x63/0xa0
 xe_driver_devcoredump_fini+0x12/0x20 [xe]
 devm_action_release+0x12/0x30
 release_nodes+0x3a/0x120
 devres_release_all+0x8a/0xd0
 device_unbind_cleanup+0x12/0x80
 device_release_driver_internal+0x23a/0x280
 ? bus_find_device+0xa8/0xe0
 device_driver_detach+0x14/0x20
 unbind_store+0xaf/0xc0
 drv_attr_store+0x21/0x50
 sysfs_kf_write+0x4a/0x80
 kernfs_fop_write_iter+0x169/0x220
 vfs_write+0x293/0x560
 ksys_write+0x72/0xf0
 __x64_sys_write+0x19/0x30
 x64_sys_call+0x2bf/0x2660
 do_syscall_64+0x93/0xb60
 ? __f_unlock_pos+0x15/0x20
 ? __x64_sys_getdents64+0x9b/0x130
 ? __pfx_filldir64+0x10/0x10
 ? do_syscall_64+0x1a2/0xb60
 ? clear_bhb_loop+0x30/0x80
 ? clear_bhb_loop+0x30/0x80
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x76e292edd574
Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 80 3d d5 ea 0e 00 00 74 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 55 48 89 e5 48 83 ec 20 48 89
RSP: 002b:00007fffe247a828 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000076e292edd574
RDX: 000000000000000c RSI: 00006267f6306063 RDI: 000000000000000b
RBP: 000000000000000c R08: 000076e292fc4b20 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00006267f6306063
R13: 000000000000000b R14: 00006267e6859c00 R15: 000076e29322a000
 </TASK>
xe 0000:03:00.0: [drm] Xe device coredump has been deleted.

Fixes: 01daccf748 ("devcoredump : Serialize devcd_del work")
Cc: Mukesh Ojha <quic_mojha@quicinc.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org # v6.1+
Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>
Cc: Matthew Brost <matthew.brost@intel.com>
Acked-by: Mukesh Ojha <mukesh.ojha@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250723142416.1020423-1-dev@lankhorst.se
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Maarten Lankhorst
2025-07-23 16:24:16 +02:00
committed by Greg Kroah-Hartman
parent 74b84d1be0
commit a91c809659
1 changed files with 83 additions and 53 deletions
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136
drivers/base/devcoredump.c
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@@ -23,50 +23,46 @@ struct devcd_entry {
void *data;
size_t datalen;
/*
* Here, mutex is required to serialize the calls to del_wk work between
* user/kernel space which happens when devcd is added with device_add()
* and that sends uevent to user space. User space reads the uevents,
* and calls to devcd_data_write() which try to modify the work which is
* not even initialized/queued from devcoredump.
* There are 2 races for which mutex is required.
*
* The first race is between device creation and userspace writing to
* schedule immediately destruction.
*
* This race is handled by arming the timer before device creation, but
* when device creation fails the timer still exists.
*
* cpu0(X) cpu1(Y)
* To solve this, hold the mutex during device_add(), and set
* init_completed on success before releasing the mutex.
*
* dev_coredump() uevent sent to user space
* device_add() ======================> user space process Y reads the
* uevents writes to devcd fd
* which results into writes to
* That way the timer will never fire until device_add() is called,
* it will do nothing if init_completed is not set. The timer is also
* cancelled in that case.
*
* devcd_data_write()
* mod_delayed_work()
* try_to_grab_pending()
* timer_delete()
* debug_assert_init()
* INIT_DELAYED_WORK()
* schedule_delayed_work()
*
*
* Also, mutex alone would not be enough to avoid scheduling of
* del_wk work after it get flush from a call to devcd_free()
* mentioned as below.
*
* disabled_store()
* devcd_free()
* mutex_lock() devcd_data_write()
* flush_delayed_work()
* mutex_unlock()
* mutex_lock()
* mod_delayed_work()
* mutex_unlock()
* So, delete_work flag is required.
* The second race involves multiple parallel invocations of devcd_free(),
* add a deleted flag so only 1 can call the destructor.
*/
struct mutex mutex;
bool delete_work;
bool init_completed, deleted;
struct module *owner;
ssize_t (*read)(char *buffer, loff_t offset, size_t count,
void *data, size_t datalen);
void (*free)(void *data);
/*
* If nothing interferes and device_add() was returns success,
* del_wk will destroy the device after the timer fires.
*
* Multiple userspace processes can interfere in the working of the timer:
* - Writing to the coredump will reschedule the timer to run immediately,
* if still armed.
*
* This is handled by using "if (cancel_delayed_work()) {
* schedule_delayed_work() }", to prevent re-arming after having
* been previously fired.
* - Writing to /sys/class/devcoredump/disabled will destroy the
* coredump synchronously.
* This is handled by using disable_delayed_work_sync(), and then
* checking if deleted flag is set with &devcd->mutex held.
*/
struct delayed_work del_wk;
struct device *failing_dev;
};
@@ -95,14 +91,27 @@ static void devcd_dev_release(struct device *dev)
kfree(devcd);
}
static void __devcd_del(struct devcd_entry *devcd)
{
devcd->deleted = true;
device_del(&devcd->devcd_dev);
put_device(&devcd->devcd_dev);
}
static void devcd_del(struct work_struct *wk)
{
struct devcd_entry *devcd;
bool init_completed;
devcd = container_of(wk, struct devcd_entry, del_wk.work);
device_del(&devcd->devcd_dev);
put_device(&devcd->devcd_dev);
/* devcd->mutex serializes against dev_coredumpm_timeout */
mutex_lock(&devcd->mutex);
init_completed = devcd->init_completed;
mutex_unlock(&devcd->mutex);
if (init_completed)
__devcd_del(devcd);
}
static ssize_t devcd_data_read(struct file *filp, struct kobject *kobj,
@@ -122,12 +131,12 @@ static ssize_t devcd_data_write(struct file *filp, struct kobject *kobj,
struct device *dev = kobj_to_dev(kobj);
struct devcd_entry *devcd = dev_to_devcd(dev);
mutex_lock(&devcd->mutex);
if (!devcd->delete_work) {
devcd->delete_work = true;
mod_delayed_work(system_wq, &devcd->del_wk, 0);
}
mutex_unlock(&devcd->mutex);
/*
* Although it's tempting to use mod_delayed work here,
* that will cause a reschedule if the timer already fired.
*/
if (cancel_delayed_work(&devcd->del_wk))
schedule_delayed_work(&devcd->del_wk, 0);
return count;
}
@@ -151,11 +160,21 @@ static int devcd_free(struct device *dev, void *data)
{
struct devcd_entry *devcd = dev_to_devcd(dev);
/*
* To prevent a race with devcd_data_write(), disable work and
* complete manually instead.
*
* We cannot rely on the return value of
* disable_delayed_work_sync() here, because it might be in the
* middle of a cancel_delayed_work + schedule_delayed_work pair.
*
* devcd->mutex here guards against multiple parallel invocations
* of devcd_free().
*/
disable_delayed_work_sync(&devcd->del_wk);
mutex_lock(&devcd->mutex);
if (!devcd->delete_work)
devcd->delete_work = true;
flush_delayed_work(&devcd->del_wk);
if (!devcd->deleted)
__devcd_del(devcd);
mutex_unlock(&devcd->mutex);
return 0;
}
@@ -179,12 +198,10 @@ static ssize_t disabled_show(const struct class *class, const struct class_attri
* put_device() <- last reference
* error = fn(dev, data) devcd_dev_release()
* devcd_free(dev, data) kfree(devcd)
* mutex_lock(&devcd->mutex);
*
*
* In the above diagram, it looks like disabled_store() would be racing with parallelly
* running devcd_del() and result in memory abort while acquiring devcd->mutex which
* is called after kfree of devcd memory after dropping its last reference with
* running devcd_del() and result in memory abort after dropping its last reference with
* put_device(). However, this will not happens as fn(dev, data) runs
* with its own reference to device via klist_node so it is not its last reference.
* so, above situation would not occur.
@@ -374,7 +391,7 @@ void dev_coredumpm_timeout(struct device *dev, struct module *owner,
devcd->read = read;
devcd->free = free;
devcd->failing_dev = get_device(dev);
devcd->delete_work = false;
devcd->deleted = false;
mutex_init(&devcd->mutex);
device_initialize(&devcd->devcd_dev);
@@ -383,8 +400,14 @@ void dev_coredumpm_timeout(struct device *dev, struct module *owner,
atomic_inc_return(&devcd_count));
devcd->devcd_dev.class = &devcd_class;
mutex_lock(&devcd->mutex);
dev_set_uevent_suppress(&devcd->devcd_dev, true);
/* devcd->mutex prevents devcd_del() completing until init finishes */
mutex_lock(&devcd->mutex);
devcd->init_completed = false;
INIT_DELAYED_WORK(&devcd->del_wk, devcd_del);
schedule_delayed_work(&devcd->del_wk, timeout);
if (device_add(&devcd->devcd_dev))
goto put_device;
@@ -401,13 +424,20 @@ void dev_coredumpm_timeout(struct device *dev, struct module *owner,
dev_set_uevent_suppress(&devcd->devcd_dev, false);
kobject_uevent(&devcd->devcd_dev.kobj, KOBJ_ADD);
INIT_DELAYED_WORK(&devcd->del_wk, devcd_del);
schedule_delayed_work(&devcd->del_wk, timeout);
/*
* Safe to run devcd_del() now that we are done with devcd_dev.
* Alternatively we could have taken a ref on devcd_dev before
* dropping the lock.
*/
devcd->init_completed = true;
mutex_unlock(&devcd->mutex);
return;
put_device:
put_device(&devcd->devcd_dev);
mutex_unlock(&devcd->mutex);
cancel_delayed_work_sync(&devcd->del_wk);
put_device(&devcd->devcd_dev);
put_module:
module_put(owner);
free: