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@xxxxxxxxx>
> Cc: Michal Wajdeczko <michal.wajdeczko@xxxxxxxxx>
> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Cc: Marta Lofstedt <marta.lofstedt@xxxxxxxxx>
> Cc: Michal Winiarski <michal.winiarski@xxxxxxxxx>
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris
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