linux-kernel - [PATCH 2/2] KHO: init new_physxa->phys

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Message-ID: <20250518142315.241670-3-changyuanl@google.com>
Date: Sun, 18 May 2025 07:23:15 -0700
From: Changyuan Lyu <changyuanl@...gle.com>
To: rppt@...nel.org, akpm@...ux-foundation.org
Cc: graf@...zon.com, bhe@...hat.com, kexec@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, chrisl@...nel.org, 
	pasha.tatashin@...een.com, jasonmiu@...gle.com, 
	Changyuan Lyu <changyuanl@...gle.com>
Subject: [PATCH 2/2] KHO: init new_physxa->phys_bits to fix lockdep

From: Pasha Tatashin <pasha.tatashin@...een.com>

Lockdep shows the following warning:

INFO: trying to register non-static key.
The code is fine but needs lockdep annotation, or maybe
you didn't initialize this object before use?
turning off the locking correctness validator.

[<ffffffff810133a6>] dump_stack_lvl+0x66/0xa0
[<ffffffff8136012c>] assign_lock_key+0x10c/0x120
[<ffffffff81358bb4>] register_lock_class+0xf4/0x2f0
[<ffffffff813597ff>] __lock_acquire+0x7f/0x2c40
[<ffffffff81360cb0>] ? __pfx_hlock_conflict+0x10/0x10
[<ffffffff811707be>] ? native_flush_tlb_global+0x8e/0xa0
[<ffffffff8117096e>] ? __flush_tlb_all+0x4e/0xa0
[<ffffffff81172fc2>] ? __kernel_map_pages+0x112/0x140
[<ffffffff813ec327>] ? xa_load_or_alloc+0x67/0xe0
[<ffffffff81359556>] lock_acquire+0xe6/0x280
[<ffffffff813ec327>] ? xa_load_or_alloc+0x67/0xe0
[<ffffffff8100b9e0>] _raw_spin_lock+0x30/0x40
[<ffffffff813ec327>] ? xa_load_or_alloc+0x67/0xe0
[<ffffffff813ec327>] xa_load_or_alloc+0x67/0xe0
[<ffffffff813eb4c0>] kho_preserve_folio+0x90/0x100
[<ffffffff813ebb7f>] __kho_finalize+0xcf/0x400
[<ffffffff813ebef4>] kho_finalize+0x34/0x70

This is becase xa has its own lock, that is not initialized in
xa_load_or_alloc.

Modifiy __kho_preserve_order(), to properly call
xa_init(&new_physxa->phys_bits);

Fixes: fc33e4b44b27 ("kexec: enable KHO support for memory preservation")
Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
Signed-off-by: Changyuan Lyu <changyuanl@...gle.com>
---
 kernel/kexec_handover.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
index 69b953551677..f0ac6a9170f8 100644
--- a/kernel/kexec_handover.c
+++ b/kernel/kexec_handover.c
@@ -144,14 +144,35 @@ static int __kho_preserve_order(struct kho_mem_track *track, unsigned long pfn,
 				unsigned int order)
 {
 	struct kho_mem_phys_bits *bits;
-	struct kho_mem_phys *physxa;
+	struct kho_mem_phys *physxa, *new_physxa;
 	const unsigned long pfn_high = pfn >> order;

 	might_sleep();

-	physxa = xa_load_or_alloc(&track->orders, order, sizeof(*physxa));
-	if (IS_ERR(physxa))
-		return PTR_ERR(physxa);
+	physxa = xa_load(&track->orders, order);
+	if (!physxa) {
+		new_physxa = kzalloc(sizeof(*physxa), GFP_KERNEL);
+		if (!new_physxa)
+			return -ENOMEM;
+
+		xa_init(&new_physxa->phys_bits);
+		physxa = xa_cmpxchg(&track->orders, order, NULL, new_physxa,
+				    GFP_KERNEL);
+		if (xa_is_err(physxa)) {
+			int err_ret = xa_err(physxa);
+
+			xa_destroy(&new_physxa->phys_bits);
+			kfree(new_physxa);
+
+			return err_ret;
+		}
+		if (physxa) {
+			xa_destroy(&new_physxa->phys_bits);
+			kfree(new_physxa);
+		} else {
+			physxa = new_physxa;
+		}
+	}

 	bits = xa_load_or_alloc(&physxa->phys_bits, pfn_high / PRESERVE_BITS,
 				sizeof(*bits));
--
2.49.0.1101.gccaa498523-goog