Hi Andi,
On 2023-08-03 8:36 a.m., Andi Shyti wrote:
Hi Zhanjun,
On Thu, Jul 27, 2023 at 01:13:23PM -0700, Zhanjun Dong wrote:
This attempts to avoid circular locking dependency between flush delayed work and intel_gt_reset.
Switched from cancel_delayed_work_sync to cancel_delayed_work, the non-sync version for reset path, it is safe as the worker has the trylock code to handle the lock; Meanwhile keep the sync version for park/fini to ensure the worker is not still running during suspend or shutdown.
Next time, please wrap the sentences to 65 characters (standing
to the e-mail netiquette, RFC1855[1]) or 70-75 characters
(standing to the kernel guidelines[2]).
[1] https://www.ietf.org/rfc/rfc1855.txt
chapter "2.1.1 For mail", page 3
[2] https://docs.kernel.org/process/submitting-patches.html
chapter "The canonical patch format"
Thanks, will be fixed in next revision.
WARNING: possible circular locking dependency detected
6.4.0-rc1-drmtip_1340-g31e3463b0edb+ #1 Not tainted
------------------------------------------------------
kms_pipe_crc_ba/6415 is trying to acquire lock:
ffff88813e6cc640 ((work_completion)(&(&guc->timestamp.work)->work)){+.+.}-{0:0}, at: __flush_work+0x42/0x530
but task is already holding lock:
ffff88813e6cce90 (>->reset.mutex){+.+.}-{3:3}, at: intel_gt_reset+0x19e/0x470 [i915]
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #3 (>->reset.mutex){+.+.}-{3:3}:
lock_acquire+0xd8/0x2d0
i915_gem_shrinker_taints_mutex+0x31/0x50 [i915]
intel_gt_init_reset+0x65/0x80 [i915]
intel_gt_common_init_early+0xe1/0x170 [i915]
intel_root_gt_init_early+0x48/0x60 [i915]
i915_driver_probe+0x671/0xcb0 [i915]
i915_pci_probe+0xdc/0x210 [i915]
pci_device_probe+0x95/0x120
really_probe+0x164/0x3c0
__driver_probe_device+0x73/0x160
driver_probe_device+0x19/0xa0
__driver_attach+0xb6/0x180
bus_for_each_dev+0x77/0xd0
bus_add_driver+0x114/0x210
driver_register+0x5b/0x110
__pfx_vgem_open+0x3/0x10 [vgem]
do_one_initcall+0x57/0x270
do_init_module+0x5f/0x220
load_module+0x1ca4/0x1f00
__do_sys_finit_module+0xb4/0x130
do_syscall_64+0x3c/0x90
entry_SYSCALL_64_after_hwframe+0x72/0xdc
-> #2 (fs_reclaim){+.+.}-{0:0}:
lock_acquire+0xd8/0x2d0
fs_reclaim_acquire+0xac/0xe0
kmem_cache_alloc+0x32/0x260
i915_vma_instance+0xb2/0xc60 [i915]
i915_gem_object_ggtt_pin_ww+0x175/0x370 [i915]
vm_fault_gtt+0x22d/0xf60 [i915]
__do_fault+0x2f/0x1d0
do_pte_missing+0x4a/0xd20
__handle_mm_fault+0x5b0/0x790
handle_mm_fault+0xa2/0x230
do_user_addr_fault+0x3ea/0xa10
exc_page_fault+0x68/0x1a0
asm_exc_page_fault+0x26/0x30
-> #1 (>->reset.backoff_srcu){++++}-{0:0}:
lock_acquire+0xd8/0x2d0
_intel_gt_reset_lock+0x57/0x330 [i915]
guc_timestamp_ping+0x35/0x130 [i915]
process_one_work+0x250/0x510
worker_thread+0x4f/0x3a0
kthread+0xff/0x130
ret_from_fork+0x29/0x50
-> #0 ((work_completion)(&(&guc->timestamp.work)->work)){+.+.}-{0:0}:
check_prev_add+0x90/0xc60
__lock_acquire+0x1998/0x2590
lock_acquire+0xd8/0x2d0
__flush_work+0x74/0x530
__cancel_work_timer+0x14f/0x1f0
intel_guc_submission_reset_prepare+0x81/0x4b0 [i915]
intel_uc_reset_prepare+0x9c/0x120 [i915]
reset_prepare+0x21/0x60 [i915]
intel_gt_reset+0x1dd/0x470 [i915]
intel_gt_reset_global+0xfb/0x170 [i915]
intel_gt_handle_error+0x368/0x420 [i915]
intel_gt_debugfs_reset_store+0x5c/0xc0 [i915]
i915_wedged_set+0x29/0x40 [i915]
simple_attr_write_xsigned.constprop.0+0xb4/0x110
full_proxy_write+0x52/0x80
vfs_write+0xc5/0x4f0
ksys_write+0x64/0xe0
do_syscall_64+0x3c/0x90
entry_SYSCALL_64_after_hwframe+0x72/0xdc
other info that might help us debug this:
Chain exists of:
(work_completion)(&(&guc->timestamp.work)->work) --> fs_reclaim --> >->reset.mutex
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(>->reset.mutex);
lock(fs_reclaim);
lock(>->reset.mutex);
lock((work_completion)(&(&guc->timestamp.work)->work));
*** DEADLOCK ***
3 locks held by kms_pipe_crc_ba/6415:
#0: ffff888101541430 (sb_writers#15){.+.+}-{0:0}, at: ksys_write+0x64/0xe0
#1: ffff888136c7eab8 (&attr->mutex){+.+.}-{3:3}, at: simple_attr_write_xsigned.constprop.0+0x47/0x110
#2: ffff88813e6cce90 (>->reset.mutex){+.+.}-{3:3}, at: intel_gt_reset+0x19e/0x470 [i915]
v2: Add sync flag to guc_cancel_busyness_worker to ensure reset path calls asynchronous cancel.
v3: Add sync flag to intel_guc_submission_disable to ensure reset path calls asynchronous cancel.
v4: Set to always sync from __uc_fini_hw path.
Thanks for taking care of this, there was a period we could see
this splatter everywhere :)
Signed-off-by: Zhanjun Dong <zhanjun.dong@xxxxxxxxx>
Cc: John Harrison <John.C.Harrison@xxxxxxxxx>
Cc: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
---
.../gpu/drm/i915/gt/uc/intel_guc_submission.c | 17 ++++++++++-------
.../gpu/drm/i915/gt/uc/intel_guc_submission.h | 2 +-
drivers/gpu/drm/i915/gt/uc/intel_uc.c | 4 ++--
3 files changed, 13 insertions(+), 10 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index a0e3ef1c65d2..ef4300246ce1 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -1357,9 +1357,12 @@ static void guc_enable_busyness_worker(struct intel_guc *guc)
mod_delayed_work(system_highpri_wq, &guc->timestamp.work, guc->timestamp.ping_delay);
}
-static void guc_cancel_busyness_worker(struct intel_guc *guc)
+static void guc_cancel_busyness_worker(struct intel_guc *guc, bool sync)
{
- cancel_delayed_work_sync(&guc->timestamp.work);
+ if (sync)
+ cancel_delayed_work_sync(&guc->timestamp.work);
+ else
+ cancel_delayed_work(&guc->timestamp.work);
The guc_cancel_busyness_worker() wrapper is made to make life
simpler, in oder not to force the caller to find
guc->timestamp.work. But if we add a true/false value, then we
make it again difficult because we need to go and check what they
mean, so that we decrease readability.
I would rather prefer something like:
static void guc_cancel_busyness_worker_sync(struct intel_guc *guc)
{
cancel_delayed_work_sync(&guc->timestamp.work);
}
static void guc_cancel_busyness_worker(struct intel_guc *guc)
{
cancel_delayed_work(&guc->timestamp.work);
}
We could perhaps improve this with defines or inlines, but I like
this way more.
What do you think?
Andi
I like this idea, will change it that way in next revision.
Regards,
Zhanjun
}
static void __reset_guc_busyness_stats(struct intel_guc *guc)
@@ -1370,7 +1373,7 @@ static void __reset_guc_busyness_stats(struct intel_guc *guc)
unsigned long flags;
ktime_t unused;
- guc_cancel_busyness_worker(guc);
+ guc_cancel_busyness_worker(guc, false);
spin_lock_irqsave(&guc->timestamp.lock, flags);
@@ -1485,7 +1488,7 @@ static int guc_init_engine_stats(struct intel_guc *guc)
static void guc_fini_engine_stats(struct intel_guc *guc)
{
- guc_cancel_busyness_worker(guc);
+ guc_cancel_busyness_worker(guc, true);
}
void intel_guc_busyness_park(struct intel_gt *gt)
@@ -1500,7 +1503,7 @@ void intel_guc_busyness_park(struct intel_gt *gt)
* and causes an unclaimed register access warning. Cancel the worker
* synchronously here.
*/
- guc_cancel_busyness_worker(guc);
+ guc_cancel_busyness_worker(guc, true);
/*
* Before parking, we should sample engine busyness stats if we need to.
@@ -4501,9 +4504,9 @@ int intel_guc_submission_enable(struct intel_guc *guc)
}
/* Note: By the time we're here, GuC may have already been reset */
-void intel_guc_submission_disable(struct intel_guc *guc)
+void intel_guc_submission_disable(struct intel_guc *guc, bool sync)
{
- guc_cancel_busyness_worker(guc);
+ guc_cancel_busyness_worker(guc, sync);
/* Semaphore interrupt disable and route to host */
guc_route_semaphores(guc, false);
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.h
index c57b29cdb1a6..a77de0d6ed58 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.h
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.h
@@ -16,7 +16,7 @@ struct intel_engine_cs;
void intel_guc_submission_init_early(struct intel_guc *guc);
int intel_guc_submission_init(struct intel_guc *guc);
int intel_guc_submission_enable(struct intel_guc *guc);
-void intel_guc_submission_disable(struct intel_guc *guc);
+void intel_guc_submission_disable(struct intel_guc *guc, bool sync);
void intel_guc_submission_fini(struct intel_guc *guc);
int intel_guc_preempt_work_create(struct intel_guc *guc);
void intel_guc_preempt_work_destroy(struct intel_guc *guc);
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc.c b/drivers/gpu/drm/i915/gt/uc/intel_uc.c
index 18250fb64bd8..5b76f0d4d2a6 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_uc.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_uc.c
@@ -566,7 +566,7 @@ static int __uc_init_hw(struct intel_uc *uc)
* We've failed to load the firmware :(
*/
err_submission:
- intel_guc_submission_disable(guc);
+ intel_guc_submission_disable(guc, true);
err_log_capture:
__uc_capture_load_err_log(uc);
err_rps:
@@ -597,7 +597,7 @@ static void __uc_fini_hw(struct intel_uc *uc)
return;
if (intel_uc_uses_guc_submission(uc))
- intel_guc_submission_disable(guc);
+ intel_guc_submission_disable(guc, true);
__uc_sanitize(uc);
}
--
2.34.1
