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Message-ID: <18af3213-6c46-4611-ba75-da5be5a1c9b0@arm.com>
Date: Wed, 14 Jan 2026 17:49:30 +0000
From: Seunguk Shin <seunguk.shin@....com>
To: linux-kernel@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org, nvdimm@...ts.linux.dev,
dan.j.williams@...el.com, willy@...radead.org, jack@...e.cz,
Nick.Connolly@....com, ffidencio@...dia.com
Subject: [PATCH] fs/dax: check zero or empty entry before converting xarray
Trying to convert zero or empty xarray entry causes kernel panic.
[ 0.737679] EXT4-fs (pmem0p1): mounted filesystem
79676804-7c8b-491a-b2a6-9bae3c72af70 ro with ordered data mode. Quota
mode: disabled.
[ 0.737891] VFS: Mounted root (ext4 filesystem) readonly on device 259:1.
[ 0.739119] devtmpfs: mounted
[ 0.739476] Freeing unused kernel memory: 1920K
[ 0.740156] Run /sbin/init as init process
[ 0.740229] with arguments:
[ 0.740286] /sbin/init
[ 0.740321] with environment:
[ 0.740369] HOME=/
[ 0.740400] TERM=linux
[ 0.743162] Unable to handle kernel paging request at virtual address
fffffdffbf000008
[ 0.743285] Mem abort info:
[ 0.743316] ESR = 0x0000000096000006
[ 0.743371] EC = 0x25: DABT (current EL), IL = 32 bits
[ 0.743444] SET = 0, FnV = 0
[ 0.743489] EA = 0, S1PTW = 0
[ 0.743545] FSC = 0x06: level 2 translation fault
[ 0.743610] Data abort info:
[ 0.743656] ISV = 0, ISS = 0x00000006, ISS2 = 0x00000000
[ 0.743720] CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[ 0.743785] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[ 0.743848] swapper pgtable: 4k pages, 48-bit VAs, pgdp=00000000b9d17000
[ 0.743931] [fffffdffbf000008] pgd=10000000bfa3d403,
p4d=10000000bfa3d403, pud=1000000040bfe403, pmd=0000000000000000
[ 0.744070] Internal error: Oops: 0000000096000006 [#1] SMP
[ 0.748888] CPU: 0 UID: 0 PID: 1 Comm: init Not tainted 6.18.4 #1 NONE
[ 0.749421] pstate: 004000c5 (nzcv daIF +PAN -UAO -TCO -DIT -SSBS
BTYPE=--)
[ 0.749969] pc : dax_disassociate_entry.constprop.0+0x20/0x50
[ 0.750444] lr : dax_insert_entry+0xcc/0x408
[ 0.750802] sp : ffff80008000b9e0
[ 0.751083] x29: ffff80008000b9e0 x28: 0000000000000000 x27:
0000000000000000
[ 0.751682] x26: 0000000001963d01 x25: ffff0000004f7d90 x24:
0000000000000000
[ 0.752264] x23: 0000000000000000 x22: ffff80008000bcc8 x21:
0000000000000011
[ 0.752836] x20: ffff80008000ba90 x19: 0000000001963d01 x18:
0000000000000000
[ 0.753407] x17: 0000000000000000 x16: 0000000000000000 x15:
0000000000000000
[ 0.753970] x14: ffffbf3154b9ae70 x13: 0000000000000000 x12:
ffffbf3154b9ae70
[ 0.754548] x11: ffffffffffffffff x10: 0000000000000000 x9 :
0000000000000000
[ 0.755122] x8 : 000000000000000d x7 : 000000000000001f x6 :
0000000000000000
[ 0.755707] x5 : 0000000000000000 x4 : 0000000000000000 x3 :
fffffdffc0000000
[ 0.756287] x2 : 0000000000000008 x1 : 0000000040000000 x0 :
fffffdffbf000000
[ 0.756871] Call trace:
[ 0.757107] dax_disassociate_entry.constprop.0+0x20/0x50 (P)
[ 0.757592] dax_iomap_pte_fault+0x4fc/0x808
[ 0.757951] dax_iomap_fault+0x28/0x30
[ 0.758258] ext4_dax_huge_fault+0x80/0x2dc
[ 0.758594] ext4_dax_fault+0x10/0x3c
[ 0.758892] __do_fault+0x38/0x12c
[ 0.759175] __handle_mm_fault+0x530/0xcf0
[ 0.759518] handle_mm_fault+0xe4/0x230
[ 0.759833] do_page_fault+0x17c/0x4dc
[ 0.760144] do_translation_fault+0x30/0x38
[ 0.760483] do_mem_abort+0x40/0x8c
[ 0.760771] el0_ia+0x4c/0x170
[ 0.761032] el0t_64_sync_handler+0xd8/0xdc
[ 0.761371] el0t_64_sync+0x168/0x16c
[ 0.761677] Code: f9453021 f2dfbfe3 cb813080 8b001860 (f9400401)
[ 0.762168] ---[ end trace 0000000000000000 ]---
[ 0.762550] note: init[1] exited with irqs disabled
[ 0.762631] Kernel panic - not syncing: Attempted to kill init!
exitcode=0x0000000b
This patch just reorders checking and converting.
Signed-off-by: Seunguk Shin <seunguk.shin@....com>
---
fs/dax.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index 289e6254aa30..de316be2cc4e 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -443,11 +443,12 @@ static void dax_associate_entry(void *entry,
struct address_space *mapping,
unsigned long address, bool shared)
{
unsigned long size = dax_entry_size(entry), index;
- struct folio *folio = dax_to_folio(entry);
+ struct folio *folio;
if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry))
return;
+ folio = dax_to_folio(entry);
index = linear_page_index(vma, address & ~(size - 1));
if (shared && (folio->mapping || dax_folio_is_shared(folio))) {
if (folio->mapping)
@@ -468,21 +469,23 @@ static void dax_associate_entry(void *entry,
struct address_space *mapping,
static void dax_disassociate_entry(void *entry, struct address_space
*mapping,
bool trunc)
{
- struct folio *folio = dax_to_folio(entry);
+ struct folio *folio;
if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry))
return;
+ folio = dax_to_folio(entry);
dax_folio_put(folio);
}
static struct page *dax_busy_page(void *entry)
{
- struct folio *folio = dax_to_folio(entry);
+ struct folio *folio;
if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry))
return NULL;
+ folio = dax_to_folio(entry);
if (folio_ref_count(folio) - folio_mapcount(folio))
return &folio->page;
else
--
2.34.1
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