On Wed, Apr 22, 2026 at 5:00 PM Lucas Oakley <soakley@redhat.com> wrote:

In RHEL 9.4 ppc64le, the stack size was adjusted
from 16k to 32k. This can cause ppc64_back_trace()
to bail prematurely since SIZE(irq_ctx), used in
ppc64_in_irqstack(), is set to 16k. This patch
ensures that irq_ctx is updated to 32k when
task_init() executes, which occurs just before
other variables are initalized using the incorrectly
sized irq_ctx.

Tested on: x86_64, s390x, aarch64, ppc64le

Without the commit:

crash> bt -c 3
PID: 17524 TASK: c0000000b2c0e400 CPU: 3 COMMAND: "xyz"
cannot find the stack info.

With the commit:

crash> bt -c 3
PID: 17524 TASK: c0000000b2c0e400 CPU: 3 COMMAND: "xyz"
#0 [c000001dff7d7c10] smp_call_function_single_async at c00000000028dd38
#1 [c000001dff7d7d30] _raw_spin_lock_irqsave at c000000001023f1c
#2 [c000001dff7d7d60] ibmvscsi_handle_crq at c0080000044635ec [ibmvscsi]
#3 [c000001dff7d7de0] ibmvscsi_task at c008000004463804 [ibmvscsi]
#4 [c000001dff7d7e30] tasklet_action_common.constprop.0 at c0000000001624cc
#5 [c000001dff7d7e90] __do_softirq at c0000000010244cc
#6 [c000001dff7d7f90] do_softirq_own_stack at c000000000016480
#7 [c000000140d67700] __irq_exit_rcu at c0000000001613b8
#8 [c000000140d67730] irq_exit at c000000000162170
#9 [c000000140d67750] do_IRQ at c000000000015fa4
#10 [c000000140d67780] hardware_interrupt_common_virt at c000000000009080
Hardware Interrupt [500] exception frame:
R0: c000000001023de0 R1: c000000140d67a90 R2: c000000002c02500
R3: c00800000b30269c R4: 0000000000000001 R5: 0000000000000001
R6: ffffffffffffffff R7: 0000000000000000 R8: 0000000000000000
R9: fffffffffffe0000 R10: 0000000000000002 R11: 0000000048422824
R12: c000000001023d70 R13: c000001dffffd480 R14: 00007ffd6ef6d238
R15: 0000000000000028 R16: c000001dfc1e2280 R17: c000001dfc1e2280
R18: 00000000ab97fa48 R19: 0000000000000000 R20: 0000000000000001
R21: 0000001df9ff0000 R22: 0000000000000028 R23: c0000000021f2280
R24: 0000000000000000 R25: c0000000021f2280 R26: c0000000021f2380
R27: 0000000000000000 R28: c00800000b30269c R29: 0000000000000000
R30: c000000002c47190 R31: 000000000020000b
NIP: c0000000000aea14 MSR: 800000000280b033 OR3: c0000000000ae944
CTR: c000000001023d70 LR: c000000001023de0 XER: 0000000020040001
CCR: 0000000088422824 MQ: 0000000000000000 DAR: 0000000000000001
DSISR: c0080000073b1e94 Syscall Result: 0000000000000000
[NIP : queued_spin_lock_slowpath+1204]
[LR : _raw_spin_lock+112]
#11 [c000000140d67a90] queued_spin_lock_slowpath at c0000000000aea14
#12 [c000000140d67bb0] _raw_spin_lock at c000000001023de0 (unreliable)
#13 [c000000140d67bd0] dm_blk_close at c00800000b2c6850 [dm_mod]
#14 [c000000140d67c00] blkdev_put_whole at c0000000007d2738
#15 [c000000140d67c30] bdev_release at c0000000007d3a38
#16 [c000000140d67c90] blkdev_release at c0000000007d4224
#17 [c000000140d67cb0] __fput at c0000000005d2e98
#18 [c000000140d67d00] task_work_run at c00000000018fb14
#19 [c000000140d67d50] do_notify_resume at c000000000020bd4
#20 [c000000140d67d80] interrupt_exit_user_prepare_main at c00000000002ed98
#21 [c000000140d67de0] syscall_exit_prepare at c00000000002f240
#22 [c000000140d67e10] system_call_vectored_common at c00000000000bff4

Signed-off-by: Lucas Oakley <soakley@redhat.com>
---
task.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/task.c b/task.c
index ec04b55..46d46bf 100644
--- a/task.c
+++ b/task.c
@@ -497,6 +497,17 @@ task_init(void)
} else if (VALID_SIZE(thread_union) &&
((len = SIZE(thread_union)) != STACKSIZE())) {
machdep->stacksize = len;
+ /*
+ * RHEL 9.4.z adjusted the stack size from 16k to 32k for
+ * ppc64le only. We need to ensure that SIZE(irq_ctx) is
+ * correctly set so the unwinder doesn't prematurely bail
+ * when switching stacks. The stack size is updated in
+ * task_init(), so ensure irq_ctx is updated here. I'm
+ * adjusting it here since allocations referencing irq_ctx
+ * can occur promptly after this point.
+ */
+ if (SIZE(irq_ctx) != -1)
+ ASSIGN_SIZE(irq_ctx) = len;
} else if (!VALID_SIZE(thread_union) && !VALID_SIZE(task_union)) {
len = 0;
if (kernel_symbol_exists("__start_init_stack") &&
--
2.52.0
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