[PATCH] drm/v3d: Assign job pointer to NULL before signaling the fence

[Maíra Canal]

On 22/01/25 22:24, Maíra Canal wrote:
> In commit e4b5ccd392b9 ("drm/v3d: Ensure job pointer is set to NULL
> after job completion"), we introduced a change to assign the job pointer
> to NULL after completing a job, indicating job completion.
> 
> However, this approach created a race condition between the DRM
> scheduler workqueue and the IRQ execution thread. As soon as the fence is
> signaled in the IRQ execution thread, a new job starts to be executed.
> This results in a race condition where the IRQ execution thread sets the
> job pointer to NULL simultaneously as the `run_job()` function assigns
> a new job to the pointer.
> 
> This race condition can lead to a NULL pointer dereference if the IRQ
> execution thread sets the job pointer to NULL after `run_job()` assigns
> it to the new job. When the new job completes and the GPU emits an
> interrupt, `v3d_irq()` is triggered, potentially causing a crash.
> 
> [  466.310099] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000c0
> [  466.318928] Mem abort info:
> [  466.321723]   ESR = 0x0000000096000005
> [  466.325479]   EC = 0x25: DABT (current EL), IL = 32 bits
> [  466.330807]   SET = 0, FnV = 0
> [  466.333864]   EA = 0, S1PTW = 0
> [  466.337010]   FSC = 0x05: level 1 translation fault
> [  466.341900] Data abort info:
> [  466.344783]   ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
> [  466.350285]   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
> [  466.355350]   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
> [  466.360677] user pgtable: 4k pages, 39-bit VAs, pgdp=0000000089772000
> [  466.367140] [00000000000000c0] pgd=0000000000000000, p4d=0000000000000000, pud=0000000000000000
> [  466.375875] Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
> [  466.382163] Modules linked in: rfcomm snd_seq_dummy snd_hrtimer snd_seq snd_seq_device algif_hash algif_skcipher af_alg bnep binfmt_misc vc4 snd_soc_hdmi_codec drm_display_helper cec brcmfmac_wcc spidev rpivid_hevc(C) drm_client_lib brcmfmac hci_uart drm_dma_helper pisp_be btbcm brcmutil snd_soc_core aes_ce_blk v4l2_mem2mem bluetooth aes_ce_cipher snd_compress videobuf2_dma_contig ghash_ce cfg80211 gf128mul snd_pcm_dmaengine videobuf2_memops ecdh_generic sha2_ce ecc videobuf2_v4l2 snd_pcm v3d sha256_arm64 rfkill videodev snd_timer sha1_ce libaes gpu_sched snd videobuf2_common sha1_generic drm_shmem_helper mc rp1_pio drm_kms_helper raspberrypi_hwmon spi_bcm2835 gpio_keys i2c_brcmstb rp1 raspberrypi_gpiomem rp1_mailbox rp1_adc nvmem_rmem uio_pdrv_genirq uio i2c_dev drm ledtrig_pattern drm_panel_orientation_quirks backlight fuse dm_mod ip_tables x_tables ipv6
> [  466.458429] CPU: 0 UID: 1000 PID: 2008 Comm: chromium Tainted: G         C         6.13.0-v8+ #18
> [  466.467336] Tainted: [C]=CRAP
> [  466.470306] Hardware name: Raspberry Pi 5 Model B Rev 1.0 (DT)
> [  466.476157] pstate: 404000c9 (nZcv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [  466.483143] pc : v3d_irq+0x118/0x2e0 [v3d]
> [  466.487258] lr : __handle_irq_event_percpu+0x60/0x228
> [  466.492327] sp : ffffffc080003ea0
> [  466.495646] x29: ffffffc080003ea0 x28: ffffff80c0c94200 x27: 0000000000000000
> [  466.502807] x26: ffffffd08dd81d7b x25: ffffff80c0c94200 x24: ffffff8003bdc200
> [  466.509969] x23: 0000000000000001 x22: 00000000000000a7 x21: 0000000000000000
> [  466.517130] x20: ffffff8041bb0000 x19: 0000000000000001 x18: 0000000000000000
> [  466.524291] x17: ffffffafadfb0000 x16: ffffffc080000000 x15: 0000000000000000
> [  466.531452] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
> [  466.538613] x11: 0000000000000000 x10: 0000000000000000 x9 : ffffffd08c527eb0
> [  466.545777] x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000
> [  466.552941] x5 : ffffffd08c4100d0 x4 : ffffffafadfb0000 x3 : ffffffc080003f70
> [  466.560102] x2 : ffffffc0829e8058 x1 : 0000000000000001 x0 : 0000000000000000
> [  466.567263] Call trace:
> [  466.569711]  v3d_irq+0x118/0x2e0 [v3d] (P)
> [  466.573826]  __handle_irq_event_percpu+0x60/0x228
> [  466.578546]  handle_irq_event+0x54/0xb8
> [  466.582391]  handle_fasteoi_irq+0xac/0x240
> [  466.586498]  generic_handle_domain_irq+0x34/0x58
> [  466.591128]  gic_handle_irq+0x48/0xd8
> [  466.594798]  call_on_irq_stack+0x24/0x58
> [  466.598730]  do_interrupt_handler+0x88/0x98
> [  466.602923]  el0_interrupt+0x44/0xc0
> [  466.606508]  __el0_irq_handler_common+0x18/0x28
> [  466.611050]  el0t_64_irq_handler+0x10/0x20
> [  466.615156]  el0t_64_irq+0x198/0x1a0
> [  466.618740] Code: 52800035 3607faf3 f9442e80 52800021 (f9406018)
> [  466.624853] ---[ end trace 0000000000000000 ]---
> [  466.629483] Kernel panic - not syncing: Oops: Fatal exception in interrupt
> [  466.636384] SMP: stopping secondary CPUs
> [  466.640320] Kernel Offset: 0x100c400000 from 0xffffffc080000000
> [  466.646259] PHYS_OFFSET: 0x0
> [  466.649141] CPU features: 0x100,00000170,00901250,0200720b
> [  466.654644] Memory Limit: none
> [  466.657706] ---[ end Kernel panic - not syncing: Oops: Fatal exception in interrupt ]---
> 
> Fix the crash by assigning the job pointer to NULL before signaling the
> fence. This ensures that the job pointer is cleared before any new job
> starts execution, preventing the race condition and the NULL pointer
> dereference crash.
> 
> Cc: stable at vger.kernel.org
> Fixes: e4b5ccd392b9 ("drm/v3d: Ensure job pointer is set to NULL after job completion")
> Signed-off-by: Maíra Canal <mcanal at igalia.com>
> ---

Applied to misc/kernel.git (drm-misc-next-fixes).

Best Regards,
- Maíra