The patch titled
Subject: panic: ensure preemption is disabled during panic()
has been added to the -mm tree. Its filename is
panic-ensure-preemption-is-disabled-during-panic.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/panic-ensure-preemption-is-disabled-during-panic.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/panic-ensure-preemption-is-disabled-during-panic.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Will Deacon <will@xxxxxxxxxx>
Subject: panic: ensure preemption is disabled during panic()
Calling 'panic()' on a kernel with CONFIG_PREEMPT=y can leave the calling
CPU in an infinite loop, but with interrupts and preemption enabled. From
this state, userspace can continue to be scheduled, despite the system
being "dead" as far as the kernel is concerned. This is easily
reproducible on arm64 when booting with "nosmp" on the command line; a
couple of shell scripts print out a periodic "Ping" message whilst another
triggers a crash by writing to /proc/sysrq-trigger:
| sysrq: Trigger a crash
| Kernel panic - not syncing: sysrq triggered crash
| CPU: 0 PID: 1 Comm: init Not tainted 5.2.15 #1
| Hardware name: linux,dummy-virt (DT)
| Call trace:
| dump_backtrace+0x0/0x148
| show_stack+0x14/0x20
| dump_stack+0xa0/0xc4
| panic+0x140/0x32c
| sysrq_handle_reboot+0x0/0x20
| __handle_sysrq+0x124/0x190
| write_sysrq_trigger+0x64/0x88
| proc_reg_write+0x60/0xa8
| __vfs_write+0x18/0x40
| vfs_write+0xa4/0x1b8
| ksys_write+0x64/0xf0
| __arm64_sys_write+0x14/0x20
| el0_svc_common.constprop.0+0xb0/0x168
| el0_svc_handler+0x28/0x78
| el0_svc+0x8/0xc
| Kernel Offset: disabled
| CPU features: 0x0002,24002004
| Memory Limit: none
| ---[ end Kernel panic - not syncing: sysrq triggered crash ]---
| Ping 2!
| Ping 1!
| Ping 1!
| Ping 2!
The issue can also be triggered on x86 kernels if CONFIG_SMP=n, otherwise
local interrupts are disabled in 'smp_send_stop()'.
Disable preemption in 'panic()' before re-enabling interrupts.
Link: http://lkml.kernel.org/r/20191002123538.22609-1-will@xxxxxxxxxx
Link: https://lore.kernel.org/r/BX1W47JXPMR8.58IYW53H6M5N@dragonstone
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Reported-by: Xogium <contact@xxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/panic.c | 1 +
1 file changed, 1 insertion(+)
--- a/kernel/panic.c~panic-ensure-preemption-is-disabled-during-panic
+++ a/kernel/panic.c
@@ -180,6 +180,7 @@ void panic(const char *fmt, ...)
* after setting panic_cpu) from invoking panic() again.
*/
local_irq_disable();
+ preempt_disable_notrace();
/*
* It's possible to come here directly from a panic-assertion and
_
Patches currently in -mm which might be from will@xxxxxxxxxx are
panic-ensure-preemption-is-disabled-during-panic.patch
