dmaengine: tegra-adma: Fix use-after-free

dmaengine: tegra-adma: Fix use-after-free

A use-after-free bug exists in the Tegra ADMA driver when audio streams
are terminated, particularly during XRUN conditions. The issue occurs
when the DMA buffer is freed by tegra_adma_terminate_all() before the
vchan completion tasklet finishes accessing it.

The race condition follows this sequence:

  1. DMA transfer completes, triggering an interrupt that schedules the
     completion tasklet (tasklet has not executed yet)
  2. Audio playback stops, calling tegra_adma_terminate_all() which
     frees the DMA buffer memory via kfree()
  3. The scheduled tasklet finally executes, calling vchan_complete()
     which attempts to access the already-freed memory

Since tasklets can execute at any time after being scheduled, there is
no guarantee that the buffer will remain valid when vchan_complete()
runs.

Fix this by properly synchronizing the virtual channel completion:
 - Calling vchan_terminate_vdesc() in tegra_adma_stop() to mark the
   descriptors as terminated instead of freeing the descriptor.
 - Add the callback tegra_adma_synchronize() that calls
   vchan_synchronize() which kills any pending tasklets and frees any
   terminated descriptors.

Crash logs:
[  337.427523] BUG: KASAN: use-after-free in vchan_complete+0x124/0x3b0
[  337.427544] Read of size 8 at addr ffff000132055428 by task swapper/0/0

[  337.427562] Call trace:
[  337.427564]  dump_backtrace+0x0/0x320
[  337.427571]  show_stack+0x20/0x30
[  337.427575]  dump_stack_lvl+0x68/0x84
[  337.427584]  print_address_description.constprop.0+0x74/0x2b8
[  337.427590]  kasan_report+0x1f4/0x210
[  337.427598]  __asan_load8+0xa0/0xd0
[  337.427603]  vchan_complete+0x124/0x3b0
[  337.427609]  tasklet_action_common.constprop.0+0x190/0x1d0
[  337.427617]  tasklet_action+0x30/0x40
[  337.427623]  __do_softirq+0x1a0/0x5c4
[  337.427628]  irq_exit+0x110/0x140
[  337.427633]  handle_domain_irq+0xa4/0xe0
[  337.427640]  gic_handle_irq+0x64/0x160
[  337.427644]  call_on_irq_stack+0x20/0x4c
[  337.427649]  do_interrupt_handler+0x7c/0x90
[  337.427654]  el1_interrupt+0x30/0x80
[  337.427659]  el1h_64_irq_handler+0x18/0x30
[  337.427663]  el1h_64_irq+0x7c/0x80
[  337.427667]  cpuidle_enter_state+0xe4/0x540
[  337.427674]  cpuidle_enter+0x54/0x80
[  337.427679]  do_idle+0x2e0/0x380
[  337.427685]  cpu_startup_entry+0x2c/0x70
[  337.427690]  rest_init+0x114/0x130
[  337.427695]  arch_call_rest_init+0x18/0x24
[  337.427702]  start_kernel+0x380/0x3b4
[  337.427706]  __primary_switched+0xc0/0xc8

Fixes: f46b195799b5 ("dmaengine: tegra-adma: Add support for Tegra210 ADMA")
Signed-off-by: Sheetal <sheetal@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Link: https://patch.msgid.link/20251110142445.3842036-1-sheetal@nvidia.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>