Centos-kernel-stream-10

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Jerome Marchand 756d361463 rcu: Fix rcu_read_unlock() deadloop due to softirq

JIRA: https://issues.redhat.com/browse/RHEL-178446

Conflicts:
 - Context change from missing commit 42d590d100f2 ("rcu: Remove
local_irq_save/restore() in rcu_preempt_deferred_qs_handler()")
 - Context change from missing commit c04507ac500e ("sched: Provide
and use set_need_resched_current()")

commit d41e37f26b3157b3f1d10223863519a943aa239b
Author: Yao Kai <yaokai34@huawei.com>
Date:   Thu Jan 1 11:34:10 2026 -0500

    rcu: Fix rcu_read_unlock() deadloop due to softirq

    Commit 5f5fa7ea89 ("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.

    Fixes: 5f5fa7ea89 ("rcu: Don't use negative nesting depth in __rcu_read_unlock()")
    Reported-by: Tengda Wu <wutengda2@huawei.com>
    Signed-off-by: Yao Kai <yaokai34@huawei.com>
    Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
    Tested-by: Paul E. McKenney <paulmck@kernel.org>
    Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
    Signed-off-by: Boqun Feng <boqun.feng@gmail.com>

(cherry picked from commit d41e37f26b3157b3f1d10223863519a943aa239b)
Assisted-by: Patchpal
Signed-off-by: Jerome Marchand <jmarchan@redhat.com>