From 77715906921251bd9f75bcf4825f176df3f91208 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Fri, 23 Aug 2019 19:14:55 +0100 Subject: [PATCH] drm/i915: Keep drm_i915_file_private around under RCU Ensure that the drm_i915_file_private continues to exist as we attempt to remove a request from its list, which may race with the destruction of the file. <6> [38.380714] [IGT] gem_ctx_create: starting subtest basic-files <0> [42.201329] BUG: spinlock bad magic on CPU#0, kworker/u16:0/7 <4> [42.201356] general protection fault: 0000 [#1] PREEMPT SMP PTI <4> [42.201371] CPU: 0 PID: 7 Comm: kworker/u16:0 Tainted: G U 5.3.0-rc5-CI-Patchwork_14169+ #1 <4> [42.201391] Hardware name: Dell Inc. OptiPlex 745 /0GW726, BIOS 2.3.1 05/21/2007 <4> [42.201594] Workqueue: i915 retire_work_handler [i915] <4> [42.201614] RIP: 0010:spin_dump+0x5a/0x90 <4> [42.201625] Code: 00 48 8d 88 c0 06 00 00 48 c7 c7 00 71 09 82 e8 35 ef 00 00 48 85 db 44 8b 4d 08 41 b8 ff ff ff ff 48 c7 c1 0b cd 0f 82 74 0e <44> 8b 83 e0 04 00 00 48 8d 8b c0 06 00 00 8b 55 04 48 89 ee 48 c7 <4> [42.201660] RSP: 0018:ffffc9000004bd80 EFLAGS: 00010202 <4> [42.201673] RAX: 0000000000000031 RBX: 6b6b6b6b6b6b6b6b RCX: ffffffff820fcd0b <4> [42.201688] RDX: 0000000000000000 RSI: ffff88803de266f8 RDI: 00000000ffffffff <4> [42.201703] RBP: ffff888038381ff8 R08: 00000000ffffffff R09: 000000006b6b6b6b <4> [42.201718] R10: 0000000041cb0b89 R11: 646162206b636f6c R12: ffff88802a618500 <4> [42.201733] R13: ffff88802b32c288 R14: ffff888038381ff8 R15: ffff88802b32c250 <4> [42.201748] FS: 0000000000000000(0000) GS:ffff88803de00000(0000) knlGS:0000000000000000 <4> [42.201765] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 <4> [42.201778] CR2: 00007f2cefc6d180 CR3: 00000000381ee000 CR4: 00000000000006f0 <4> [42.201793] Call Trace: <4> [42.201805] do_raw_spin_lock+0x66/0xb0 <4> [42.201898] i915_request_retire+0x548/0x7c0 [i915] <4> [42.201989] retire_requests+0x4d/0x60 [i915] <4> [42.202078] i915_retire_requests+0x144/0x2e0 [i915] <4> [42.202169] retire_work_handler+0x10/0x40 [i915] Recently, in commit 44c22f3f1a0a ("drm/i915: Serialize insertion into the file->mm.request_list"), we fixed a race on insertion. Now, it appears we also have a race with destruction! Signed-off-by: Chris Wilson Cc: Matthew Auld Reviewed-by: Matthew Auld Link: https://patchwork.freedesktop.org/patch/msgid/20190823181455.31910-1-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/gem/i915_gem_throttle.c | 4 +--- drivers/gpu/drm/i915/i915_drv.c | 2 +- drivers/gpu/drm/i915/i915_drv.h | 6 +++++- drivers/gpu/drm/i915/i915_request.c | 13 +++++++------ 4 files changed, 14 insertions(+), 11 deletions(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_throttle.c b/drivers/gpu/drm/i915/gem/i915_gem_throttle.c index 1e37242..540ef05 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_throttle.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_throttle.c @@ -50,10 +50,8 @@ i915_gem_throttle_ioctl(struct drm_device *dev, void *data, if (time_after_eq(request->emitted_jiffies, recent_enough)) break; - if (target) { + if (target && xchg(&target->file_priv, NULL)) list_del(&target->client_link); - target->file_priv = NULL; - } target = request; } diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c index b5b2a64..723b9b7 100644 --- a/drivers/gpu/drm/i915/i915_drv.c +++ b/drivers/gpu/drm/i915/i915_drv.c @@ -1730,7 +1730,7 @@ static void i915_driver_postclose(struct drm_device *dev, struct drm_file *file) i915_gem_release(dev, file); mutex_unlock(&dev->struct_mutex); - kfree(file_priv); + kfree_rcu(file_priv, rcu); /* Catch up with all the deferred frees from "this" client */ i915_gem_flush_free_objects(to_i915(dev)); diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index ba3f6d8..f5e39a3 100644 --- a/drivers/gpu/drm/i915/i915_drv.h +++ b/drivers/gpu/drm/i915/i915_drv.h @@ -185,7 +185,11 @@ struct i915_mmu_object; struct drm_i915_file_private { struct drm_i915_private *dev_priv; - struct drm_file *file; + + union { + struct drm_file *file; + struct rcu_head rcu; + }; struct { spinlock_t lock; diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index a53777d..18865ce 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -169,16 +169,17 @@ remove_from_client(struct i915_request *request) { struct drm_i915_file_private *file_priv; - file_priv = READ_ONCE(request->file_priv); - if (!file_priv) + if (!READ_ONCE(request->file_priv)) return; - spin_lock(&file_priv->mm.lock); - if (request->file_priv) { + rcu_read_lock(); + file_priv = xchg(&request->file_priv, NULL); + if (file_priv) { + spin_lock(&file_priv->mm.lock); list_del(&request->client_link); - request->file_priv = NULL; + spin_unlock(&file_priv->mm.lock); } - spin_unlock(&file_priv->mm.lock); + rcu_read_unlock(); } static void free_capture_list(struct i915_request *request) -- 2.7.4