rcu: Fix rcu_read_unlock() deadloop due to softirq

In the Linux kernel, the following vulnerability has been resolved:

rcu: Fix rcu_read_unlock() deadloop due to softirq

Commit 5f5fa7ea89dc ("rcu: Don't use negative nesting depth in

__rcu_read_unlock()") removes the recursion-protection code from

__rcu_read_unlock(). Therefore, we could invoke the deadloop in

raise_softirq_irqoff() with ftrace enabled as follows:

WARNING: CPU: 0 PID: 0 at kernel/trace/trace.c:3021 __ftrace_trace_stack.constprop.0+0x172/0x180

Modules linked in: my_irq_work(O)

CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Tainted: G O 6.18.0-rc7-dirty #23 PREEMPT(full)

Tainted: [O]=OOT_MODULE

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014

RIP: 0010:__ftrace_trace_stack.constprop.0+0x172/0x180

RSP: 0018:ffffc900000034a8 EFLAGS: 00010002

RAX: 0000000000000000 RBX: 0000000000000004 RCX: 0000000000000000

RDX: 0000000000000003 RSI: ffffffff826d7b87 RDI: ffffffff826e9329

RBP: 0000000000090009 R08: 0000000000000005 R09: ffffffff82afbc4c

R10: 0000000000000008 R11: 0000000000011d7a R12: 0000000000000000

R13: ffff888003874100 R14: 0000000000000003 R15: ffff8880038c1054

FS: 0000000000000000(0000) GS:ffff8880fa8ea000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 000055b31fa7f540 CR3: 00000000078f4005 CR4: 0000000000770ef0

PKRU: 55555554

Call Trace:

<IRQ>

trace_buffer_unlock_commit_regs+0x6d/0x220

trace_event_buffer_commit+0x5c/0x260

trace_event_raw_event_softirq+0x47/0x80

raise_softirq_irqoff+0x6e/0xa0

rcu_read_unlock_special+0xb1/0x160

unwind_next_frame+0x203/0x9b0

__unwind_start+0x15d/0x1c0

arch_stack_walk+0x62/0xf0

stack_trace_save+0x48/0x70

__ftrace_trace_stack.constprop.0+0x144/0x180

trace_buffer_unlock_commit_regs+0x6d/0x220

trace_event_buffer_commit+0x5c/0x260

trace_event_raw_event_softirq+0x47/0x80

raise_softirq_irqoff+0x6e/0xa0

rcu_read_unlock_special+0xb1/0x160

unwind_next_frame+0x203/0x9b0

__unwind_start+0x15d/0x1c0

arch_stack_walk+0x62/0xf0

stack_trace_save+0x48/0x70

__ftrace_trace_stack.constprop.0+0x144/0x180

trace_buffer_unlock_commit_regs+0x6d/0x220

trace_event_buffer_commit+0x5c/0x260

trace_event_raw_event_softirq+0x47/0x80

raise_softirq_irqoff+0x6e/0xa0

rcu_read_unlock_special+0xb1/0x160

unwind_next_frame+0x203/0x9b0

__unwind_start+0x15d/0x1c0

arch_stack_walk+0x62/0xf0

stack_trace_save+0x48/0x70

__ftrace_trace_stack.constprop.0+0x144/0x180

trace_buffer_unlock_commit_regs+0x6d/0x220

trace_event_buffer_commit+0x5c/0x260

trace_event_raw_event_softirq+0x47/0x80

raise_softirq_irqoff+0x6e/0xa0

rcu_read_unlock_special+0xb1/0x160

__is_insn_slot_addr+0x54/0x70

kernel_text_address+0x48/0xc0

__kernel_text_address+0xd/0x40

unwind_get_return_address+0x1e/0x40

arch_stack_walk+0x9c/0xf0

stack_trace_save+0x48/0x70

__ftrace_trace_stack.constprop.0+0x144/0x180

trace_buffer_unlock_commit_regs+0x6d/0x220

trace_event_buffer_commit+0x5c/0x260

trace_event_raw_event_softirq+0x47/0x80

__raise_softirq_irqoff+0x61/0x80

__flush_smp_call_function_queue+0x115/0x420

__sysvec_call_function_single+0x17/0xb0

sysvec_call_function_single+0x8c/0xc0

</IRQ>

Commit b41642c87716 ("rcu: Fix rcu_read_unlock() deadloop due to IRQ work")

fixed the infinite loop in rcu_read_unlock_special() for IRQ work by

setting a flag before calling irq_work_queue_on(). We fix this issue by

setting the same flag before calling raise_softirq_irqoff() and rename the

flag to defer_qs_pending for more common.