An unlikely ABBA deadlock in debugfs that no one has reported.
[ 284.922349] ======================================================
[ 284.922355] [ INFO: possible circular locking dependency detected ]
[ 284.922361] 4.8.0-rc2+ #430 Tainted: G W
[ 284.922366] -------------------------------------------------------
[ 284.922371] cat/1197 is trying to acquire lock:
[ 284.922376] (&dev->filelist_mutex){+.+...}, at: [<ffffffffa0055ba2>] i915_ppgtt_info+0x82/0x390 [i915]
[ 284.922423]
[ 284.922423] but task is already holding lock:
[ 284.922429] (&dev->struct_mutex){+.+.+.}, at: [<ffffffffa0055b55>] i915_ppgtt_info+0x35/0x390 [i915]
[ 284.922465]
[ 284.922465] which lock already depends on the new lock.
[ 284.922465]
[ 284.922471]
[ 284.922471] the existing dependency chain (in reverse order) is:
[ 284.922477]
-> #1 (&dev->struct_mutex){+.+.+.}:
[ 284.922493] [<ffffffff81087710>] lock_acquire+0x60/0x80
[ 284.922505] [<ffffffff8143e96f>] mutex_lock_nested+0x5f/0x360
[ 284.922520] [<ffffffffa004f877>] print_context_stats+0x37/0xf0 [i915]
[ 284.922549] [<ffffffffa00535f5>] i915_gem_object_info+0x265/0x490 [i915]
[ 284.922581] [<ffffffff81144491>] seq_read+0xe1/0x3b0
[ 284.922592] [<ffffffff811f77b3>] full_proxy_read+0x83/0xb0
[ 284.922604] [<ffffffff8111ba03>] __vfs_read+0x23/0x110
[ 284.922616] [<ffffffff8111c9b9>] vfs_read+0x89/0x110
[ 284.922626] [<ffffffff8111dbf4>] SyS_read+0x44/0xa0
[ 284.922636] [<ffffffff81442be9>] entry_SYSCALL_64_fastpath+0x1c/0xac
[ 284.922648]
-> #0 (&dev->filelist_mutex){+.+...}:
[ 284.922667] [<ffffffff810871fc>] __lock_acquire+0x10fc/0x1270
[ 284.922678] [<ffffffff81087710>] lock_acquire+0x60/0x80
[ 284.922689] [<ffffffff8143e96f>] mutex_lock_nested+0x5f/0x360
[ 284.922701] [<ffffffffa0055ba2>] i915_ppgtt_info+0x82/0x390 [i915]
[ 284.922729] [<ffffffff81144491>] seq_read+0xe1/0x3b0
[ 284.922739] [<ffffffff811f77b3>] full_proxy_read+0x83/0xb0
[ 284.922750] [<ffffffff8111ba03>] __vfs_read+0x23/0x110
[ 284.922761] [<ffffffff8111c9b9>] vfs_read+0x89/0x110
[ 284.922771] [<ffffffff8111dbf4>] SyS_read+0x44/0xa0
[ 284.922781] [<ffffffff81442be9>] entry_SYSCALL_64_fastpath+0x1c/0xac
[ 284.922793]
[ 284.922793] other info that might help us debug this:
[ 284.922793]
[ 284.922809] Possible unsafe locking scenario:
[ 284.922809]
[ 284.922818] CPU0 CPU1
[ 284.922825] ---- ----
[ 284.922831] lock(&dev->struct_mutex);
[ 284.922842] lock(&dev->filelist_mutex);
[ 284.922854] lock(&dev->struct_mutex);
[ 284.922865] lock(&dev->filelist_mutex);
[ 284.922875]
[ 284.922875] *** DEADLOCK ***
[ 284.922875]
[ 284.922888] 3 locks held by cat/1197:
[ 284.922895] #0: (debugfs_srcu){......}, at: [<ffffffff811f7730>] full_proxy_read+0x0/0xb0
[ 284.922919] #1: (&p->lock){+.+.+.}, at: [<ffffffff811443e8>] seq_read+0x38/0x3b0
[ 284.922942] #2: (&dev->struct_mutex){+.+.+.}, at: [<ffffffffa0055b55>] i915_ppgtt_info+0x35/0x390 [i915]
[ 284.922983]
Fixes: 1d2ac403ae3b ("drm: Protect dev->filelist with its own mutex")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_debugfs.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 1bc07576d675..7d7b4d9280e9 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -2270,10 +2270,13 @@ static int i915_ppgtt_info(struct seq_file *m, void *data)
struct drm_i915_private *dev_priv = node_to_i915(m->private);
struct drm_device *dev = &dev_priv->drm;
struct drm_file *file;
+ int ret;
- int ret = mutex_lock_interruptible(&dev->struct_mutex);
+ mutex_lock(&dev->filelist_mutex);
+ ret = mutex_lock_interruptible(&dev->struct_mutex);
if (ret)
- return ret;
+ goto out_unlock;
+
intel_runtime_pm_get(dev_priv);
if (INTEL_GEN(dev_priv) >= 8)
@@ -2281,7 +2284,6 @@ static int i915_ppgtt_info(struct seq_file *m, void *data)
else if (INTEL_GEN(dev_priv) >= 6)
gen6_ppgtt_info(m, dev_priv);
- mutex_lock(&dev->filelist_mutex);
list_for_each_entry_reverse(file, &dev->filelist, lhead) {
struct drm_i915_file_private *file_priv = file->driver_priv;
struct task_struct *task;
@@ -2289,19 +2291,19 @@ static int i915_ppgtt_info(struct seq_file *m, void *data)
task = get_pid_task(file->pid, PIDTYPE_PID);
if (!task) {
ret = -ESRCH;
- goto out_unlock;
+ goto out_rpm;
}
seq_printf(m, "\nproc: %s\n", task->comm);
put_task_struct(task);
idr_for_each(&file_priv->context_idr, per_file_ctx,
(void *)(unsigned long)m);
}
-out_unlock:
- mutex_unlock(&dev->filelist_mutex);
+out_rpm:
intel_runtime_pm_put(dev_priv);
mutex_unlock(&dev->struct_mutex);
-
+out_unlock:
+ mutex_unlock(&dev->filelist_mutex);
return ret;
}
--
2.9.3
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