[PATCH] kexec: Fix reboot race during device_shutdown()

[Joel Fernandes (Google)]

During kexec reboot, it is possible for a race to occur between
device_shutdown() and userspace.  This causes accesses to GPU after pm_runtime
suspend has already happened. Fix this by calling freeze_processes() before
device_shutdown().

Such freezing is already being done if kernel supports KEXEC_JUMP and
kexec_image->preserve_context is true. However, doing it if either of these are
not true prevents crashes/races.

This fixes the following crash during kexec reboot on an ARM64 device
with adreno GPU:

[  292.534314] Kernel panic - not syncing: Asynchronous SError Interrupt
[  292.534323] Hardware name: Google Lazor (rev3 - 8) with LTE (DT)
[  292.534326] Call trace:
[  292.534328]  dump_backtrace+0x0/0x1d4
[  292.534337]  show_stack+0x20/0x2c
[  292.534342]  dump_stack_lvl+0x60/0x78
[  292.534347]  dump_stack+0x18/0x38
[  292.534352]  panic+0x148/0x3b0
[  292.534357]  nmi_panic+0x80/0x94
[  292.534364]  arm64_serror_panic+0x70/0x7c
[  292.534369]  do_serror+0x0/0x7c
[  292.534372]  do_serror+0x54/0x7c
[  292.534377]  el1h_64_error_handler+0x34/0x4c
[  292.534381]  el1h_64_error+0x7c/0x80
[  292.534386]  el1_interrupt+0x20/0x58
[  292.534389]  el1h_64_irq_handler+0x18/0x24
[  292.534395]  el1h_64_irq+0x7c/0x80
[  292.534399]  local_daif_inherit+0x10/0x18
[  292.534405]  el1h_64_sync_handler+0x48/0xb4
[  292.534410]  el1h_64_sync+0x7c/0x80
[  292.534414]  a6xx_gmu_set_oob+0xbc/0x1fc
[  292.534422]  a6xx_get_timestamp+0x40/0xb4
[  292.534426]  adreno_get_param+0x12c/0x1e0
[  292.534433]  msm_ioctl_get_param+0x64/0x70
[  292.534440]  drm_ioctl_kernel+0xe8/0x158
[  292.534448]  drm_ioctl+0x208/0x320
[  292.534453]  __arm64_sys_ioctl+0x98/0xd0
[  292.534461]  invoke_syscall+0x4c/0x118

Cc: Steven Rostedt <rostedt at goodmis.org>
Cc: Ricardo Ribalda <ribalda at google.com>
Cc: Ross Zwisler <zwisler at google.com>
Cc: Rob Clark <robdclark at gmail.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Tested-by: Ricardo Ribalda <ribalda at google.com>
Signed-off-by: Joel Fernandes (Google) <joel at joelfernandes.org>
---
 kernel/kexec_core.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index e2f2574d8b74..6599f485e42d 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -1299,6 +1299,12 @@ int kernel_kexec(void)
 	} else
 #endif
 	{
+		error = freeze_processes();
+		if (error) {
+			error = -EBUSY;
+			goto Unlock;
+		}
+
 		kexec_in_progress = true;
 		kernel_restart_prepare("kexec reboot");
 		migrate_to_reboot_cpu();
-- 
2.42.0.582.g8ccd20d70d-goog