[v4,3/6] drm/i915/guc: Fix lockdep due to log relay channel handling under struct_mutex
diff mbox

Message ID 1516808821-3638-3-git-send-email-sagar.a.kamble@intel.com
State New
Headers show

Commit Message

sagar.a.kamble@intel.com Jan. 24, 2018, 3:46 p.m. UTC
This patch fixes lockdep issue due to circular locking dependency of
struct_mutex, i_mutex_key, mmap_sem, relay_channels_mutex.
For GuC log relay channel we create debugfs file that requires i_mutex_key
lock and we are doing that under struct_mutex. So we introduced newer
dependency as:
    &dev->struct_mutex --> &sb->s_type->i_mutex_key#3 --> &mm->mmap_sem
However, there is dependency from mmap_sem to struct_mutex. Hence we
separate the relay create/destroy operation from under struct_mutex.
Also added runtime check of relay buffer status.

Comments

Chris Wilson Jan. 24, 2018, 7:40 p.m. UTC | #1
Quoting Sagar Arun Kamble (2018-01-24 15:46:58)
> This patch fixes lockdep issue due to circular locking dependency of
> struct_mutex, i_mutex_key, mmap_sem, relay_channels_mutex.
> For GuC log relay channel we create debugfs file that requires i_mutex_key
> lock and we are doing that under struct_mutex. So we introduced newer
> dependency as:
>     &dev->struct_mutex --> &sb->s_type->i_mutex_key#3 --> &mm->mmap_sem
> However, there is dependency from mmap_sem to struct_mutex. Hence we
> separate the relay create/destroy operation from under struct_mutex.
> Also added runtime check of relay buffer status.
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.15.0-rc6-CI-Patchwork_7614+ #1 Not tainted
> ------------------------------------------------------
> debugfs_test/1388 is trying to acquire lock:
>  (&dev->struct_mutex){+.+.}, at: [<00000000d5e1d915>] i915_mutex_lock_interruptible+0x47/0x130 [i915]
> 
> but task is already holding lock:
>  (&mm->mmap_sem){++++}, at: [<0000000029a9c131>] __do_page_fault+0x106/0x560
> 
> which lock already depends on the new lock.
> 
> the existing dependency chain (in reverse order) is:
> 
> -> #3 (&mm->mmap_sem){++++}:
>        _copy_to_user+0x1e/0x70
>        filldir+0x8c/0xf0
>        dcache_readdir+0xeb/0x160
>        iterate_dir+0xdc/0x140
>        SyS_getdents+0xa0/0x130
>        entry_SYSCALL_64_fastpath+0x1c/0x89
> 
> -> #2 (&sb->s_type->i_mutex_key#3){++++}:
>        start_creating+0x59/0x110
>        __debugfs_create_file+0x2e/0xe0
>        relay_create_buf_file+0x62/0x80
>        relay_late_setup_files+0x84/0x250
>        guc_log_late_setup+0x4f/0x110 [i915]
>        i915_guc_log_register+0x32/0x40 [i915]
>        i915_driver_load+0x7b6/0x1720 [i915]
>        i915_pci_probe+0x2e/0x90 [i915]
>        pci_device_probe+0x9c/0x120
>        driver_probe_device+0x2a3/0x480
>        __driver_attach+0xd9/0xe0
>        bus_for_each_dev+0x57/0x90
>        bus_add_driver+0x168/0x260
>        driver_register+0x52/0xc0
>        do_one_initcall+0x39/0x150
>        do_init_module+0x56/0x1ef
>        load_module+0x231c/0x2d70
>        SyS_finit_module+0xa5/0xe0
>        entry_SYSCALL_64_fastpath+0x1c/0x89
> 
> -> #1 (relay_channels_mutex){+.+.}:
>        relay_open+0x12c/0x2b0
>        intel_guc_log_runtime_create+0xab/0x230 [i915]
>        intel_guc_init+0x81/0x120 [i915]
>        intel_uc_init+0x29/0xa0 [i915]
>        i915_gem_init+0x182/0x530 [i915]
>        i915_driver_load+0xaa9/0x1720 [i915]
>        i915_pci_probe+0x2e/0x90 [i915]
>        pci_device_probe+0x9c/0x120
>        driver_probe_device+0x2a3/0x480
>        __driver_attach+0xd9/0xe0
>        bus_for_each_dev+0x57/0x90
>        bus_add_driver+0x168/0x260
>        driver_register+0x52/0xc0
>        do_one_initcall+0x39/0x150
>        do_init_module+0x56/0x1ef
>        load_module+0x231c/0x2d70
>        SyS_finit_module+0xa5/0xe0
>        entry_SYSCALL_64_fastpath+0x1c/0x89
> 
> -> #0 (&dev->struct_mutex){+.+.}:
>        __mutex_lock+0x81/0x9b0
>        i915_mutex_lock_interruptible+0x47/0x130 [i915]
>        i915_gem_fault+0x201/0x790 [i915]
>        __do_fault+0x15/0x70
>        __handle_mm_fault+0x677/0xdc0
>        handle_mm_fault+0x14f/0x2f0
>        __do_page_fault+0x2d1/0x560
>        page_fault+0x4c/0x60
> 
> other info that might help us debug this:
> 
> Chain exists of:
>   &dev->struct_mutex --> &sb->s_type->i_mutex_key#3 --> &mm->mmap_sem
> 
>  Possible unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(&mm->mmap_sem);
>                                lock(&sb->s_type->i_mutex_key#3);
>                                lock(&mm->mmap_sem);
>   lock(&dev->struct_mutex);
> 
>  *** DEADLOCK ***
> 
> 1 lock held by debugfs_test/1388:
>  #0:  (&mm->mmap_sem){++++}, at: [<0000000029a9c131>] __do_page_fault+0x106/0x560
> 
> stack backtrace:
> CPU: 2 PID: 1388 Comm: debugfs_test Not tainted 4.15.0-rc6-CI-Patchwork_7614+ #1
> Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./J4205-ITX, BIOS P1.10 09/29/2016
> Call Trace:
>  dump_stack+0x5f/0x86
>  print_circular_bug.isra.18+0x1d0/0x2c0
>  __lock_acquire+0x14ae/0x1b60
>  ? lock_acquire+0xaf/0x200
>  lock_acquire+0xaf/0x200
>  ? i915_mutex_lock_interruptible+0x47/0x130 [i915]
>  __mutex_lock+0x81/0x9b0
>  ? i915_mutex_lock_interruptible+0x47/0x130 [i915]
>  ? i915_mutex_lock_interruptible+0x47/0x130 [i915]
>  ? i915_mutex_lock_interruptible+0x47/0x130 [i915]
>  i915_mutex_lock_interruptible+0x47/0x130 [i915]
>  ? __pm_runtime_resume+0x4f/0x80
>  i915_gem_fault+0x201/0x790 [i915]
>  __do_fault+0x15/0x70
>  ? _raw_spin_unlock+0x29/0x40
>  __handle_mm_fault+0x677/0xdc0
>  handle_mm_fault+0x14f/0x2f0
>  __do_page_fault+0x2d1/0x560
>  ? page_fault+0x36/0x60
>  page_fault+0x4c/0x60
> 
> v2: Added lock protection to guc->log.runtime.relay_chan (Chris)
>     Fixed locking inside guc_flush_logs uncovered by new lockdep.
> 
> v3: Locking guc_read_update_log_buffer entirely with relay_lock. (Chris)
>     Prepared intel_guc_init_early. Moved relay_lock inside relay_create
>     relay_destroy, relay_file_create, guc_read_update_log_buffer. (Michal)
>     Removed struct_mutex lock around guc_log_flush and removed usage
>     of guc_log_has_relay() from runtime_create path as it needs
>     struct_mutex lock.
> 
> v4: Handle NULL relay sub buffer pointer earlier in read_update_log_buffer
>     (Chris). Fixed comment suffix **/. (Michal)
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104693
> Testcase: igt/debugfs_test/read_all_entries # with enable_guc=1 and guc_log_level=1
> Signed-off-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
> Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Marta Lofstedt <marta.lofstedt@intel.com>
> Cc: Michal Winiarski <michal.winiarski@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
-Chris

Patch
diff mbox

======================================================
WARNING: possible circular locking dependency detected
4.15.0-rc6-CI-Patchwork_7614+ #1 Not tainted
------------------------------------------------------
debugfs_test/1388 is trying to acquire lock:
 (&dev->struct_mutex){+.+.}, at: [<00000000d5e1d915>] i915_mutex_lock_interruptible+0x47/0x130 [i915]

but task is already holding lock:
 (&mm->mmap_sem){++++}, at: [<0000000029a9c131>] __do_page_fault+0x106/0x560

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (&mm->mmap_sem){++++}:
       _copy_to_user+0x1e/0x70
       filldir+0x8c/0xf0
       dcache_readdir+0xeb/0x160
       iterate_dir+0xdc/0x140
       SyS_getdents+0xa0/0x130
       entry_SYSCALL_64_fastpath+0x1c/0x89

-> #2 (&sb->s_type->i_mutex_key#3){++++}:
       start_creating+0x59/0x110
       __debugfs_create_file+0x2e/0xe0
       relay_create_buf_file+0x62/0x80
       relay_late_setup_files+0x84/0x250
       guc_log_late_setup+0x4f/0x110 [i915]
       i915_guc_log_register+0x32/0x40 [i915]
       i915_driver_load+0x7b6/0x1720 [i915]
       i915_pci_probe+0x2e/0x90 [i915]
       pci_device_probe+0x9c/0x120
       driver_probe_device+0x2a3/0x480
       __driver_attach+0xd9/0xe0
       bus_for_each_dev+0x57/0x90
       bus_add_driver+0x168/0x260
       driver_register+0x52/0xc0
       do_one_initcall+0x39/0x150
       do_init_module+0x56/0x1ef
       load_module+0x231c/0x2d70
       SyS_finit_module+0xa5/0xe0
       entry_SYSCALL_64_fastpath+0x1c/0x89

-> #1 (relay_channels_mutex){+.+.}:
       relay_open+0x12c/0x2b0
       intel_guc_log_runtime_create+0xab/0x230 [i915]
       intel_guc_init+0x81/0x120 [i915]
       intel_uc_init+0x29/0xa0 [i915]
       i915_gem_init+0x182/0x530 [i915]
       i915_driver_load+0xaa9/0x1720 [i915]
       i915_pci_probe+0x2e/0x90 [i915]
       pci_device_probe+0x9c/0x120
       driver_probe_device+0x2a3/0x480
       __driver_attach+0xd9/0xe0
       bus_for_each_dev+0x57/0x90
       bus_add_driver+0x168/0x260
       driver_register+0x52/0xc0
       do_one_initcall+0x39/0x150
       do_init_module+0x56/0x1ef
       load_module+0x231c/0x2d70
       SyS_finit_module+0xa5/0xe0
       entry_SYSCALL_64_fastpath+0x1c/0x89

-> #0 (&dev->struct_mutex){+.+.}:
       __mutex_lock+0x81/0x9b0
       i915_mutex_lock_interruptible+0x47/0x130 [i915]
       i915_gem_fault+0x201/0x790 [i915]
       __do_fault+0x15/0x70
       __handle_mm_fault+0x677/0xdc0
       handle_mm_fault+0x14f/0x2f0
       __do_page_fault+0x2d1/0x560
       page_fault+0x4c/0x60

other info that might help us debug this:

Chain exists of:
  &dev->struct_mutex --> &sb->s_type->i_mutex_key#3 --> &mm->mmap_sem

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&mm->mmap_sem);
                               lock(&sb->s_type->i_mutex_key#3);
                               lock(&mm->mmap_sem);
  lock(&dev->struct_mutex);

 *** DEADLOCK ***

1 lock held by debugfs_test/1388:
 #0:  (&mm->mmap_sem){++++}, at: [<0000000029a9c131>] __do_page_fault+0x106/0x560

stack backtrace:
CPU: 2 PID: 1388 Comm: debugfs_test Not tainted 4.15.0-rc6-CI-Patchwork_7614+ #1
Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./J4205-ITX, BIOS P1.10 09/29/2016
Call Trace:
 dump_stack+0x5f/0x86
 print_circular_bug.isra.18+0x1d0/0x2c0
 __lock_acquire+0x14ae/0x1b60
 ? lock_acquire+0xaf/0x200
 lock_acquire+0xaf/0x200
 ? i915_mutex_lock_interruptible+0x47/0x130 [i915]
 __mutex_lock+0x81/0x9b0
 ? i915_mutex_lock_interruptible+0x47/0x130 [i915]
 ? i915_mutex_lock_interruptible+0x47/0x130 [i915]
 ? i915_mutex_lock_interruptible+0x47/0x130 [i915]
 i915_mutex_lock_interruptible+0x47/0x130 [i915]
 ? __pm_runtime_resume+0x4f/0x80
 i915_gem_fault+0x201/0x790 [i915]
 __do_fault+0x15/0x70
 ? _raw_spin_unlock+0x29/0x40
 __handle_mm_fault+0x677/0xdc0
 handle_mm_fault+0x14f/0x2f0
 __do_page_fault+0x2d1/0x560
 ? page_fault+0x36/0x60
 page_fault+0x4c/0x60

v2: Added lock protection to guc->log.runtime.relay_chan (Chris)
    Fixed locking inside guc_flush_logs uncovered by new lockdep.

v3: Locking guc_read_update_log_buffer entirely with relay_lock. (Chris)
    Prepared intel_guc_init_early. Moved relay_lock inside relay_create
    relay_destroy, relay_file_create, guc_read_update_log_buffer. (Michal)
    Removed struct_mutex lock around guc_log_flush and removed usage
    of guc_log_has_relay() from runtime_create path as it needs
    struct_mutex lock.

v4: Handle NULL relay sub buffer pointer earlier in read_update_log_buffer
    (Chris). Fixed comment suffix **/. (Michal)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104693
Testcase: igt/debugfs_test/read_all_entries # with enable_guc=1 and guc_log_level=1
Signed-off-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Marta Lofstedt <marta.lofstedt@intel.com>
Cc: Michal Winiarski <michal.winiarski@intel.com>
---
 drivers/gpu/drm/i915/i915_debugfs.c  |  12 +--
 drivers/gpu/drm/i915/i915_drv.c      |   2 +-
 drivers/gpu/drm/i915/i915_gem.c      |   4 +-
 drivers/gpu/drm/i915/intel_guc.c     |   7 +-
 drivers/gpu/drm/i915/intel_guc_log.c | 171 ++++++++++++++++++++++++++---------
 drivers/gpu/drm/i915/intel_guc_log.h |  12 +++
 drivers/gpu/drm/i915/intel_uc.c      |  26 +++++-
 drivers/gpu/drm/i915/intel_uc.h      |   4 +-
 8 files changed, 172 insertions(+), 66 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 80dc679..b45be0d 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -2467,7 +2467,6 @@  static int i915_guc_log_control_get(void *data, u64 *val)
 static int i915_guc_log_control_set(void *data, u64 val)
 {
 	struct drm_i915_private *dev_priv = data;
-	int ret;
 
 	if (!HAS_GUC(dev_priv))
 		return -ENODEV;
@@ -2475,16 +2474,7 @@  static int i915_guc_log_control_set(void *data, u64 val)
 	if (!dev_priv->guc.log.vma)
 		return -EINVAL;
 
-	ret = mutex_lock_interruptible(&dev_priv->drm.struct_mutex);
-	if (ret)
-		return ret;
-
-	intel_runtime_pm_get(dev_priv);
-	ret = i915_guc_log_control(dev_priv, val);
-	intel_runtime_pm_put(dev_priv);
-
-	mutex_unlock(&dev_priv->drm.struct_mutex);
-	return ret;
+	return i915_guc_log_control(dev_priv, val);
 }
 
 DEFINE_SIMPLE_ATTRIBUTE(i915_guc_log_control_fops,
diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 95e1c16..1ec12ad 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -626,7 +626,7 @@  static void i915_gem_fini(struct drm_i915_private *dev_priv)
 	i915_gem_contexts_fini(dev_priv);
 	mutex_unlock(&dev_priv->drm.struct_mutex);
 
-	intel_uc_fini_wq(dev_priv);
+	intel_uc_fini_misc(dev_priv);
 	i915_gem_cleanup_userptr(dev_priv);
 
 	i915_gem_drain_freed_objects(dev_priv);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 7f0684c..34d0d51 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -5193,7 +5193,7 @@  int i915_gem_init(struct drm_i915_private *dev_priv)
 	if (ret)
 		return ret;
 
-	ret = intel_uc_init_wq(dev_priv);
+	ret = intel_uc_init_misc(dev_priv);
 	if (ret)
 		return ret;
 
@@ -5289,7 +5289,7 @@  int i915_gem_init(struct drm_i915_private *dev_priv)
 	intel_uncore_forcewake_put(dev_priv, FORCEWAKE_ALL);
 	mutex_unlock(&dev_priv->drm.struct_mutex);
 
-	intel_uc_fini_wq(dev_priv);
+	intel_uc_fini_misc(dev_priv);
 
 	if (ret != -EIO)
 		i915_gem_cleanup_userptr(dev_priv);
diff --git a/drivers/gpu/drm/i915/intel_guc.c b/drivers/gpu/drm/i915/intel_guc.c
index ea30e7c..21140cc 100644
--- a/drivers/gpu/drm/i915/intel_guc.c
+++ b/drivers/gpu/drm/i915/intel_guc.c
@@ -64,6 +64,7 @@  void intel_guc_init_early(struct intel_guc *guc)
 {
 	intel_guc_fw_init_early(guc);
 	intel_guc_ct_init_early(&guc->ct);
+	intel_guc_log_init_early(guc);
 
 	mutex_init(&guc->send_mutex);
 	guc->send = intel_guc_send_nop;
@@ -87,8 +88,10 @@  int intel_guc_init_wq(struct intel_guc *guc)
 	 */
 	guc->log.runtime.flush_wq = alloc_ordered_workqueue("i915-guc_log",
 						WQ_HIGHPRI | WQ_FREEZABLE);
-	if (!guc->log.runtime.flush_wq)
+	if (!guc->log.runtime.flush_wq) {
+		DRM_ERROR("Couldn't allocate workqueue for GuC log\n");
 		return -ENOMEM;
+	}
 
 	/*
 	 * Even though both sending GuC action, and adding a new workitem to
@@ -109,6 +112,8 @@  int intel_guc_init_wq(struct intel_guc *guc)
 							  WQ_HIGHPRI);
 		if (!guc->preempt_wq) {
 			destroy_workqueue(guc->log.runtime.flush_wq);
+			DRM_ERROR("Couldn't allocate workqueue for GuC "
+				  "preemption\n");
 			return -ENOMEM;
 		}
 	}
diff --git a/drivers/gpu/drm/i915/intel_guc_log.c b/drivers/gpu/drm/i915/intel_guc_log.c
index 8f2da30..d10ec53 100644
--- a/drivers/gpu/drm/i915/intel_guc_log.c
+++ b/drivers/gpu/drm/i915/intel_guc_log.c
@@ -153,6 +153,8 @@  static int guc_log_relay_file_create(struct intel_guc *guc)
 	if (!i915_modparams.guc_log_level)
 		return 0;
 
+	mutex_lock(&guc->log.runtime.relay_lock);
+
 	/* For now create the log file in /sys/kernel/debug/dri/0 dir */
 	log_dir = dev_priv->drm.primary->debugfs_root;
 
@@ -169,16 +171,26 @@  static int guc_log_relay_file_create(struct intel_guc *guc)
 	 */
 	if (!log_dir) {
 		DRM_ERROR("Debugfs dir not available yet for GuC log file\n");
-		return -ENODEV;
+		ret = -ENODEV;
+		goto out_unlock;
 	}
 
 	ret = relay_late_setup_files(guc->log.runtime.relay_chan, "guc_log", log_dir);
 	if (ret < 0 && ret != -EEXIST) {
 		DRM_ERROR("Couldn't associate relay chan with file %d\n", ret);
-		return ret;
+		goto out_unlock;
 	}
 
-	return 0;
+out_unlock:
+	mutex_unlock(&guc->log.runtime.relay_lock);
+	return ret;
+}
+
+static bool guc_log_has_relay(struct intel_guc *guc)
+{
+	lockdep_assert_held(&guc->log.runtime.relay_lock);
+
+	return guc->log.runtime.relay_chan != NULL;
 }
 
 static void guc_move_to_next_buf(struct intel_guc *guc)
@@ -188,6 +200,9 @@  static void guc_move_to_next_buf(struct intel_guc *guc)
 	 */
 	smp_wmb();
 
+	if (!guc_log_has_relay(guc))
+		return;
+
 	/* All data has been written, so now move the offset of sub buffer. */
 	relay_reserve(guc->log.runtime.relay_chan, guc->log.vma->obj->base.size);
 
@@ -197,7 +212,7 @@  static void guc_move_to_next_buf(struct intel_guc *guc)
 
 static void *guc_get_write_buffer(struct intel_guc *guc)
 {
-	if (!guc->log.runtime.relay_chan)
+	if (!guc_log_has_relay(guc))
 		return NULL;
 
 	/* Just get the base address of a new sub buffer and copy data into it
@@ -265,9 +280,22 @@  static void guc_read_update_log_buffer(struct intel_guc *guc)
 	/* Get the pointer to shared GuC log buffer */
 	log_buf_state = src_data = guc->log.runtime.buf_addr;
 
+	mutex_lock(&guc->log.runtime.relay_lock);
+
 	/* Get the pointer to local buffer to store the logs */
 	log_buf_snapshot_state = dst_data = guc_get_write_buffer(guc);
 
+	if (unlikely(!log_buf_snapshot_state)) {
+		/* Used rate limited to avoid deluge of messages, logs might be
+		 * getting consumed by User at a slow rate.
+		 */
+		DRM_ERROR_RATELIMITED("no sub-buffer to capture logs\n");
+		guc->log.capture_miss_count++;
+		mutex_unlock(&guc->log.runtime.relay_lock);
+
+		return;
+	}
+
 	/* Actual logs are present from the 2nd page */
 	src_data += PAGE_SIZE;
 	dst_data += PAGE_SIZE;
@@ -293,9 +321,6 @@  static void guc_read_update_log_buffer(struct intel_guc *guc)
 		log_buf_state->flush_to_file = 0;
 		log_buf_state++;
 
-		if (unlikely(!log_buf_snapshot_state))
-			continue;
-
 		/* First copy the state structure in snapshot buffer */
 		memcpy(log_buf_snapshot_state, &log_buf_state_local,
 		       sizeof(struct guc_log_buffer_state));
@@ -335,15 +360,9 @@  static void guc_read_update_log_buffer(struct intel_guc *guc)
 		dst_data += buffer_size;
 	}
 
-	if (log_buf_snapshot_state)
-		guc_move_to_next_buf(guc);
-	else {
-		/* Used rate limited to avoid deluge of messages, logs might be
-		 * getting consumed by User at a slow rate.
-		 */
-		DRM_ERROR_RATELIMITED("no sub-buffer to capture logs\n");
-		guc->log.capture_miss_count++;
-	}
+	guc_move_to_next_buf(guc);
+
+	mutex_unlock(&guc->log.runtime.relay_lock);
 }
 
 static void capture_logs_work(struct work_struct *work)
@@ -363,8 +382,6 @@  static int guc_log_runtime_create(struct intel_guc *guc)
 {
 	struct drm_i915_private *dev_priv = guc_to_i915(guc);
 	void *vaddr;
-	struct rchan *guc_log_relay_chan;
-	size_t n_subbufs, subbuf_size;
 	int ret;
 
 	lockdep_assert_held(&dev_priv->drm.struct_mutex);
@@ -387,8 +404,44 @@  static int guc_log_runtime_create(struct intel_guc *guc)
 
 	guc->log.runtime.buf_addr = vaddr;
 
+	return 0;
+}
+
+static void guc_log_runtime_destroy(struct intel_guc *guc)
+{
+	/*
+	 * It's possible that the runtime stuff was never allocated because
+	 * GuC log was disabled at the boot time.
+	 */
+	if (!guc_log_has_runtime(guc))
+		return;
+
+	i915_gem_object_unpin_map(guc->log.vma->obj);
+	guc->log.runtime.buf_addr = NULL;
+}
+
+void intel_guc_log_init_early(struct intel_guc *guc)
+{
+	mutex_init(&guc->log.runtime.relay_lock);
+	INIT_WORK(&guc->log.runtime.flush_work, capture_logs_work);
+}
+
+int intel_guc_log_relay_create(struct intel_guc *guc)
+{
+	struct drm_i915_private *dev_priv = guc_to_i915(guc);
+	struct rchan *guc_log_relay_chan;
+	size_t n_subbufs, subbuf_size;
+	int ret;
+
+	if (!i915_modparams.guc_log_level)
+		return 0;
+
+	mutex_lock(&guc->log.runtime.relay_lock);
+
+	GEM_BUG_ON(guc_log_has_relay(guc));
+
 	 /* Keep the size of sub buffers same as shared log buffer */
-	subbuf_size = guc->log.vma->obj->base.size;
+	subbuf_size = GUC_LOG_SIZE;
 
 	/* Store up to 8 snapshots, which is large enough to buffer sufficient
 	 * boot time logs and provides enough leeway to User, in terms of
@@ -407,33 +460,39 @@  static int guc_log_runtime_create(struct intel_guc *guc)
 		DRM_ERROR("Couldn't create relay chan for GuC logging\n");
 
 		ret = -ENOMEM;
-		goto err_vaddr;
+		goto err;
 	}
 
 	GEM_BUG_ON(guc_log_relay_chan->subbuf_size < subbuf_size);
 	guc->log.runtime.relay_chan = guc_log_relay_chan;
 
-	INIT_WORK(&guc->log.runtime.flush_work, capture_logs_work);
+	mutex_unlock(&guc->log.runtime.relay_lock);
+
 	return 0;
 
-err_vaddr:
-	i915_gem_object_unpin_map(guc->log.vma->obj);
-	guc->log.runtime.buf_addr = NULL;
+err:
+	mutex_unlock(&guc->log.runtime.relay_lock);
+	/* logging will be off */
+	i915_modparams.guc_log_level = 0;
 	return ret;
 }
 
-static void guc_log_runtime_destroy(struct intel_guc *guc)
+void intel_guc_log_relay_destroy(struct intel_guc *guc)
 {
+	mutex_lock(&guc->log.runtime.relay_lock);
+
 	/*
-	 * It's possible that the runtime stuff was never allocated because
+	 * It's possible that the relay was never allocated because
 	 * GuC log was disabled at the boot time.
 	 */
-	if (!guc_log_has_runtime(guc))
-		return;
+	if (!guc_log_has_relay(guc))
+		goto out_unlock;
 
 	relay_close(guc->log.runtime.relay_chan);
-	i915_gem_object_unpin_map(guc->log.vma->obj);
-	guc->log.runtime.buf_addr = NULL;
+	guc->log.runtime.relay_chan = NULL;
+
+out_unlock:
+	mutex_unlock(&guc->log.runtime.relay_lock);
 }
 
 static int guc_log_late_setup(struct intel_guc *guc)
@@ -441,17 +500,24 @@  static int guc_log_late_setup(struct intel_guc *guc)
 	struct drm_i915_private *dev_priv = guc_to_i915(guc);
 	int ret;
 
-	lockdep_assert_held(&dev_priv->drm.struct_mutex);
-
 	if (!guc_log_has_runtime(guc)) {
 		/*
 		 * If log was disabled at boot time, then setup needed to handle
 		 * log buffer flush interrupts would not have been done yet, so
 		 * do that now.
 		 */
-		ret = guc_log_runtime_create(guc);
+		ret = intel_guc_log_relay_create(guc);
 		if (ret)
 			goto err;
+
+		mutex_lock(&dev_priv->drm.struct_mutex);
+		intel_runtime_pm_get(dev_priv);
+		ret = guc_log_runtime_create(guc);
+		intel_runtime_pm_put(dev_priv);
+		mutex_unlock(&dev_priv->drm.struct_mutex);
+
+		if (ret)
+			goto err_relay;
 	}
 
 	ret = guc_log_relay_file_create(guc);
@@ -461,7 +527,11 @@  static int guc_log_late_setup(struct intel_guc *guc)
 	return 0;
 
 err_runtime:
+	mutex_lock(&dev_priv->drm.struct_mutex);
 	guc_log_runtime_destroy(guc);
+	mutex_unlock(&dev_priv->drm.struct_mutex);
+err_relay:
+	intel_guc_log_relay_destroy(guc);
 err:
 	/* logging will remain off */
 	i915_modparams.guc_log_level = 0;
@@ -490,7 +560,11 @@  static void guc_flush_logs(struct intel_guc *guc)
 		return;
 
 	/* First disable the interrupts, will be renabled afterwards */
+	mutex_lock(&dev_priv->drm.struct_mutex);
+	intel_runtime_pm_get(dev_priv);
 	gen9_disable_guc_interrupts(dev_priv);
+	intel_runtime_pm_put(dev_priv);
+	mutex_unlock(&dev_priv->drm.struct_mutex);
 
 	/* Before initiating the forceful flush, wait for any pending/ongoing
 	 * flush to complete otherwise forceful flush may not actually happen.
@@ -498,7 +572,9 @@  static void guc_flush_logs(struct intel_guc *guc)
 	flush_work(&guc->log.runtime.flush_work);
 
 	/* Ask GuC to update the log buffer state */
+	intel_runtime_pm_get(dev_priv);
 	guc_log_flush(guc);
+	intel_runtime_pm_put(dev_priv);
 
 	/* GuC would have updated log buffer by now, so capture it */
 	guc_log_capture_logs(guc);
@@ -509,17 +585,10 @@  int intel_guc_log_create(struct intel_guc *guc)
 	struct i915_vma *vma;
 	unsigned long offset;
 	u32 flags;
-	u32 size;
 	int ret;
 
 	GEM_BUG_ON(guc->log.vma);
 
-	/* The first page is to save log buffer state. Allocate one
-	 * extra page for others in case for overlap */
-	size = (1 + GUC_LOG_DPC_PAGES + 1 +
-		GUC_LOG_ISR_PAGES + 1 +
-		GUC_LOG_CRASH_PAGES + 1) << PAGE_SHIFT;
-
 	/* We require SSE 4.1 for fast reads from the GuC log buffer and
 	 * it should be present on the chipsets supporting GuC based
 	 * submisssions.
@@ -529,7 +598,7 @@  int intel_guc_log_create(struct intel_guc *guc)
 		goto err;
 	}
 
-	vma = intel_guc_allocate_vma(guc, size);
+	vma = intel_guc_allocate_vma(guc, GUC_LOG_SIZE);
 	if (IS_ERR(vma)) {
 		ret = PTR_ERR(vma);
 		goto err;
@@ -584,7 +653,15 @@  int i915_guc_log_control(struct drm_i915_private *dev_priv, u64 control_val)
 		return 0;
 
 	verbosity = enable_logging ? control_val - 1 : 0;
+
+	ret = mutex_lock_interruptible(&dev_priv->drm.struct_mutex);
+	if (ret)
+		return ret;
+	intel_runtime_pm_get(dev_priv);
 	ret = guc_log_control(guc, enable_logging, verbosity);
+	intel_runtime_pm_put(dev_priv);
+	mutex_unlock(&dev_priv->drm.struct_mutex);
+
 	if (ret < 0) {
 		DRM_DEBUG_DRIVER("guc_logging_control action failed %d\n", ret);
 		return ret;
@@ -605,7 +682,11 @@  int i915_guc_log_control(struct drm_i915_private *dev_priv, u64 control_val)
 		}
 
 		/* GuC logging is currently the only user of Guc2Host interrupts */
+		mutex_lock(&dev_priv->drm.struct_mutex);
+		intel_runtime_pm_get(dev_priv);
 		gen9_enable_guc_interrupts(dev_priv);
+		intel_runtime_pm_put(dev_priv);
+		mutex_unlock(&dev_priv->drm.struct_mutex);
 	} else {
 		/*
 		 * Once logging is disabled, GuC won't generate logs & send an
@@ -627,13 +708,13 @@  void i915_guc_log_register(struct drm_i915_private *dev_priv)
 	if (!USES_GUC_SUBMISSION(dev_priv) || !i915_modparams.guc_log_level)
 		return;
 
-	mutex_lock(&dev_priv->drm.struct_mutex);
 	guc_log_late_setup(&dev_priv->guc);
-	mutex_unlock(&dev_priv->drm.struct_mutex);
 }
 
 void i915_guc_log_unregister(struct drm_i915_private *dev_priv)
 {
+	struct intel_guc *guc = &dev_priv->guc;
+
 	if (!USES_GUC_SUBMISSION(dev_priv))
 		return;
 
@@ -643,6 +724,8 @@  void i915_guc_log_unregister(struct drm_i915_private *dev_priv)
 	gen9_disable_guc_interrupts(dev_priv);
 	intel_runtime_pm_put(dev_priv);
 
-	guc_log_runtime_destroy(&dev_priv->guc);
+	guc_log_runtime_destroy(guc);
 	mutex_unlock(&dev_priv->drm.struct_mutex);
+
+	intel_guc_log_relay_destroy(guc);
 }
diff --git a/drivers/gpu/drm/i915/intel_guc_log.h b/drivers/gpu/drm/i915/intel_guc_log.h
index f512cf7..c638b9d 100644
--- a/drivers/gpu/drm/i915/intel_guc_log.h
+++ b/drivers/gpu/drm/i915/intel_guc_log.h
@@ -32,6 +32,13 @@ 
 struct drm_i915_private;
 struct intel_guc;
 
+/*
+ * The first page is to save log buffer state. Allocate one
+ * extra page for others in case for overlap
+ */
+#define GUC_LOG_SIZE	((1 + GUC_LOG_DPC_PAGES + 1 + GUC_LOG_ISR_PAGES + \
+			  1 + GUC_LOG_CRASH_PAGES + 1) << PAGE_SHIFT)
+
 struct intel_guc_log {
 	u32 flags;
 	struct i915_vma *vma;
@@ -41,6 +48,8 @@  struct intel_guc_log {
 		struct workqueue_struct *flush_wq;
 		struct work_struct flush_work;
 		struct rchan *relay_chan;
+		/* To serialize the access to relay_chan */
+		struct mutex relay_lock;
 	} runtime;
 	/* logging related stats */
 	u32 capture_miss_count;
@@ -52,6 +61,9 @@  struct intel_guc_log {
 
 int intel_guc_log_create(struct intel_guc *guc);
 void intel_guc_log_destroy(struct intel_guc *guc);
+void intel_guc_log_init_early(struct intel_guc *guc);
+int intel_guc_log_relay_create(struct intel_guc *guc);
+void intel_guc_log_relay_destroy(struct intel_guc *guc);
 int i915_guc_log_control(struct drm_i915_private *dev_priv, u64 control_val);
 void i915_guc_log_register(struct drm_i915_private *dev_priv);
 void i915_guc_log_unregister(struct drm_i915_private *dev_priv);
diff --git a/drivers/gpu/drm/i915/intel_uc.c b/drivers/gpu/drm/i915/intel_uc.c
index f78a17b..e3f3509 100644
--- a/drivers/gpu/drm/i915/intel_uc.c
+++ b/drivers/gpu/drm/i915/intel_uc.c
@@ -236,28 +236,44 @@  static void guc_disable_communication(struct intel_guc *guc)
 	guc->send = intel_guc_send_nop;
 }
 
-int intel_uc_init_wq(struct drm_i915_private *dev_priv)
+int intel_uc_init_misc(struct drm_i915_private *dev_priv)
 {
+	struct intel_guc *guc = &dev_priv->guc;
 	int ret;
 
 	if (!USES_GUC(dev_priv))
 		return 0;
 
-	ret = intel_guc_init_wq(&dev_priv->guc);
+	ret = intel_guc_init_wq(guc);
 	if (ret) {
 		DRM_ERROR("Couldn't allocate workqueues for GuC\n");
-		return ret;
+		goto err;
+	}
+
+	ret = intel_guc_log_relay_create(guc);
+	if (ret) {
+		DRM_ERROR("Couldn't allocate relay for GuC log\n");
+		goto err_relay;
 	}
 
 	return 0;
+
+err_relay:
+	intel_guc_fini_wq(guc);
+err:
+	return ret;
 }
 
-void intel_uc_fini_wq(struct drm_i915_private *dev_priv)
+void intel_uc_fini_misc(struct drm_i915_private *dev_priv)
 {
+	struct intel_guc *guc = &dev_priv->guc;
+
 	if (!USES_GUC(dev_priv))
 		return;
 
-	intel_guc_fini_wq(&dev_priv->guc);
+	intel_guc_fini_wq(guc);
+
+	intel_guc_log_relay_destroy(guc);
 }
 
 int intel_uc_init(struct drm_i915_private *dev_priv)
diff --git a/drivers/gpu/drm/i915/intel_uc.h b/drivers/gpu/drm/i915/intel_uc.h
index 8a72497..f2984e0 100644
--- a/drivers/gpu/drm/i915/intel_uc.h
+++ b/drivers/gpu/drm/i915/intel_uc.h
@@ -33,8 +33,8 @@ 
 void intel_uc_init_mmio(struct drm_i915_private *dev_priv);
 void intel_uc_init_fw(struct drm_i915_private *dev_priv);
 void intel_uc_fini_fw(struct drm_i915_private *dev_priv);
-int intel_uc_init_wq(struct drm_i915_private *dev_priv);
-void intel_uc_fini_wq(struct drm_i915_private *dev_priv);
+int intel_uc_init_misc(struct drm_i915_private *dev_priv);
+void intel_uc_fini_misc(struct drm_i915_private *dev_priv);
 int intel_uc_init_hw(struct drm_i915_private *dev_priv);
 void intel_uc_fini_hw(struct drm_i915_private *dev_priv);
 int intel_uc_init(struct drm_i915_private *dev_priv);