• Sagar Arun Kamble's avatar
    drm/i915/guc: Fix lockdep due to log relay channel handling under struct_mutex · 70deeadd
    Sagar Arun Kamble authored
    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.
    Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    
    ======================================================
    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: default avatarSagar 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>
    Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Link: https://patchwork.freedesktop.org/patch/msgid/1516808821-3638-3-git-send-email-sagar.a.kamble@intel.com
    70deeadd
i915_debugfs.c 133 KB