FAILED: patch "[PATCH] mm, swap: ratelimit bad swap entry reports" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x f9dc428249ed962a70acf301f01eae8578449161
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090322-mating-twice-bdd0@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f9dc428249ed962a70acf301f01eae8578449161 Mon Sep 17 00:00:00 2001
From: Breno Leitao <[email protected]>
Date: Tue, 18 Aug 2026 02:03:40 -0700
Subject: [PATCH] mm, swap: ratelimit bad swap entry reports

A corrupt page table hands the same bogus entry to get_swap_device() on every access to the mapping, and every rejection is logged. One machine logged 6185620 copies of the same line in a few hours.

swap_dup_entry_direct() prints the same message from the fork path, once per call: the WARN_ON_ONCE() guarding it warns once, the pr_err() inside does not.

Rate limit all three prints.

index dacef34a3ed7..53bf01d5f7f1 100644
@@ -1899,11 +1899,11 @@ struct swap_info_struct *get_swap_device(swp_entry_t entry)
 
 	return si;
 bad_nofile:
-	pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val);
+	pr_err_ratelimited("%s: %s%08lx\n", __func__, Bad_file, entry.val);
 out:
 	return NULL;
 put_out:
-	pr_err("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
+	pr_err_ratelimited("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
 	percpu_ref_put(&si->users);
 	return NULL;
 }

@@ -3883,7 +3883,7 @@ int swap_dup_entry_direct(swp_entry_t entry)
 
 	si = swap_entry_to_info(entry);
 	if (WARN_ON_ONCE(!si)) {
-		pr_err("%s%08lx\n", Bad_file, entry.val);
+		pr_err_ratelimited("%s%08lx\n", Bad_file, entry.val);
 		return -EINVAL;
 	}
 

From: gao xu <[email protected]>

[ Upstream commit c3e998398de48a7528842f05858a3a6bb21002e6 ]

Add a NULL check on the return value of swp_swap_info in __swap_duplicate to prevent crashes caused by NULL pointer dereference.

The reason why swp_swap_info() returns NULL is unclear; it may be due to CPU cache issues or DDR bit flips. The probability of this issue is very small - it has been observed to occur approximately 1 in 500,000 times per week. The stack info we encountered is as follows:

Unable to handle kernel NULL pointer dereference at virtual address

0000000000000058
[RB/E]rb_sreason_str_set: sreason_str set null_pointer Mem abort info:
ESR = 0x0000000096000005
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x05: level 1 translation fault
Data abort info:
ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
CM = 0, WnR = 0, TnD = 0, TagAccess = 0
GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
user pgtable: 4k pages, 39-bit VAs, pgdp=00000008a80e5000 [0000000000000058] pgd=0000000000000000, p4d=0000000000000000, pud=0000000000000000

Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
Skip md ftrace buffer dump for: 0x1609e0
...
pc : swap_duplicate+0x44/0x164
lr : copy_page_range+0x508/0x1e78

sp : ffffffc0f2a699e0
x29: ffffffc0f2a699e0 x28: ffffff8a5b28d388 x27: ffffff8b06603388
x26: ffffffdf7291fe70 x25: 0000000000000006 x24: 0000000000100073
x23: 00000000002d2d2f x22: 0000000000000008 x21: 0000000000000000
x20: 00000000002d2d2f x19: 18000000002d2d2f x18: ffffffdf726faec0
x17: 0000000000000000 x16: 0010000000000001 x15: 0040000000000001
x14: 0400000000000001 x13: ff7ffffffffffb7f x12: ffeffffffffffbff
x11: ffffff8a5c7e1898 x10: 0000000000000018 x9 : 0000000000000006 x8 : 1800000000000000 x7 : 0000000000000000 x6 : ffffff8057c01f10 x5 : 000000000000a318 x4 : 0000000000000000 x3 : 0000000000000000 x2 : 0000006daf200000 x1 : 0000000000000001 x0 : 18000000002d2d2f

Call trace:
 swap_duplicate+0x44/0x164
 copy_page_range+0x508/0x1e78
 copy_process+0x1278/0x21cc
 kernel_clone+0x90/0x438
 __arm64_sys_clone+0x5c/0x8c
 invoke_syscall+0x58/0x110
 do_el0_svc+0x8c/0xe0
 el0_svc+0x38/0x9c
 el0t_64_sync_handler+0x44/0xec
 el0t_64_sync+0x1a8/0x1ac
Code: 9139c35a 71006f3f 54000568 f8797b55 (f9402ea8)
---[ end trace 0000000000000000 ]---
Kernel panic - not syncing: Oops: Fatal exception

SMP: stopping secondary CPUs

The patch seems to only provide a workaround, but there are no more effective software solutions to handle the bit flips problem. This path will change the issue from a system crash to a process exception, thereby reducing the impact on the entire machine.

akpm: this is probably a kernel bug, but this patch keeps the system running and doesn't reduce that bug's debuggability.

Stable-dep-of: f9dc428249ed ("mm, swap: ratelimit bad swap entry reports")

---
 mm/swapfile.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

index 53637144c18e5..49ad86d543f92 100644
@@ -3283,21 +3283,26 @@ void si_swapinfo(struct sysinfo *val)
  * - swap-cache reference is requested but the entry is not used. -> ENOENT
  * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
  */
+#define swap_entry_to_info swp_swap_info
 static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
 {
-	struct swap_info_struct *p;
+	struct swap_info_struct *si;
 	struct swap_cluster_info *ci;
 	unsigned long offset;
 	unsigned char count;
 	unsigned char has_cache;
 	int err;
 
-	p = swp_swap_info(entry);
+	si = swap_entry_to_info(entry);
+	if (WARN_ON_ONCE(!si)) {
+		pr_err_ratelimited("%s%08lx\n", Bad_file, entry.val);
+		return -EINVAL;
+	}
 
 	offset = swp_offset(entry);
-	ci = lock_cluster_or_swap_info(p, offset);
+	ci = lock_cluster_or_swap_info(si, offset);
 
-	count = p->swap_map[offset];
+	count = si->swap_map[offset];
 
 	/*
 	 * swapin_readahead() doesn't check if a swap entry is valid, so the

@@ -3328,19 +3333,20 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
 			count += usage;
 		else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
 			err = -EINVAL;
-		else if (swap_count_continued(p, offset, count))
+		else if (swap_count_continued(si, offset, count))
 			count = COUNT_CONTINUED;
 		else
 			err = -ENOMEM;
 	} else
 		err = -ENOENT;			/* unused swap entry */
 
-	WRITE_ONCE(p->swap_map[offset], count | has_cache);
+	WRITE_ONCE(si->swap_map[offset], count | has_cache);
 
 unlock_out:
-	unlock_cluster_or_swap_info(p, ci);
+	unlock_cluster_or_swap_info(si, ci);
 	return err;
 }
+#undef swap_entry_to_info
 
 /*
  * Help swapoff by noting that swap entry belongs to shmem/tmpfs

2.53.0

From: Breno Leitao <[email protected]>

[ Upstream commit f9dc428249ed962a70acf301f01eae8578449161 ]

A corrupt page table hands the same bogus entry to get_swap_device() on every access to the mapping, and every rejection is logged. One machine logged 6185620 copies of the same line in a few hours.

swap_dup_entry_direct() prints the same message from the fork path, once per call: the WARN_ON_ONCE() guarding it warns once, the pr_err() inside does not.

Rate limit all three prints.

---
 mm/swapfile.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 49ad86d543f92..965bb1ed3372f 100644
@@ -1284,11 +1284,11 @@ struct swap_info_struct *get_swap_device(swp_entry_t entry)
 
 	return si;
 bad_nofile:
-	pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val);
+	pr_err_ratelimited("%s: %s%08lx\n", __func__, Bad_file, entry.val);
 out:
 	return NULL;
 put_out:
-	pr_err("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
+	pr_err_ratelimited("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
 	percpu_ref_put(&si->users);
 	return NULL;
 }

2.53.0