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ARC: show_regs: lockdep: re-enable preemption

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[ Upstream commit f731a8e89f8c78985707c626680f3e24c7a60772 ]

signal handling core calls show_regs() with preemption disabled which
on ARC takes mmap_sem for mm/vma access, causing lockdep splat.

| [ARCLinux]# ./segv-null-ptr
| potentially unexpected fatal signal 11.
| BUG: sleeping function called from invalid context at kernel/fork.c:1011
| in_atomic(): 1, irqs_disabled(): 0, pid: 70, name: segv-null-ptr
| no locks held by segv-null-ptr/70.
| CPU: 0 PID: 70 Comm: segv-null-ptr Not tainted 4.18.0+ #69
|
| Stack Trace:
|  arc_unwind_core+0xcc/0x100
|  ___might_sleep+0x17a/0x190
|  mmput+0x16/0xb8
|  show_regs+0x52/0x310
|  get_signal+0x5ee/0x610
|  do_signal+0x2c/0x218
|  resume_user_mode_begin+0x90/0xd8

Workaround by re-enabling preemption temporarily.

Note that the preemption disabling in core code around show_regs()
was introduced by commit 3a9f84d354ce ("signals, debug: fix BUG: using
smp_processor_id() in preemptible code in print_fatal_signal()")

to silence a differnt lockdep seen on x86 bakc in 2009.

Cc: <stable@vger.kernel.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Vineet Gupta 2018-12-18 10:39:58 -08:00 committed by Greg Kroah-Hartman
parent 424b75b799
commit 96af7d92d8
1 changed files with 8 additions and 0 deletions
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8
arch/arc/kernel/troubleshoot.c
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@ -179,6 +179,12 @@ void show_regs(struct pt_regs *regs)
struct task_struct *tsk = current;
struct callee_regs *cregs;
/*
* generic code calls us with preemption disabled, but some calls
* here could sleep, so re-enable to avoid lockdep splat
*/
preempt_enable();
print_task_path_n_nm(tsk);
show_regs_print_info(KERN_INFO);
@ -221,6 +227,8 @@ void show_regs(struct pt_regs *regs)
cregs = (struct callee_regs *)current->thread.callee_reg;
if (cregs)
show_callee_regs(cregs);
preempt_disable();
}
void show_kernel_fault_diag(const char *str, struct pt_regs *regs,