The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: 24963ae1b0b6596dc36e352c18593800056251d8
Gitweb: https://git.kernel.org/tip/24963ae1b0b6596dc36e352c18593800056251d8
Author: Suchit Karunakaran <suchitkarunakaran(a)gmail.com>
AuthorDate: Sat, 16 Aug 2025 12:21:26 +05:30
Committer: Dave Hansen <dave.hansen(a)linux.intel.com>
CommitterDate: Mon, 25 Aug 2025 08:23:37 -07:00
x86/cpu/intel: Fix the constant_tsc model check for Pentium 4
Pentium 4's which are INTEL_P4_PRESCOTT (model 0x03) and later have
a constant TSC. This was correctly captured until commit fadb6f569b10
("x86/cpu/intel: Limit the non-architectural constant_tsc model checks").
In that commit, an error was introduced while selecting the last P4
model (0x06) as the upper bound. Model 0x06 was transposed to
INTEL_P4_WILLAMETTE, which is just plain wrong. That was presumably a
simple typo, probably just copying and pasting the wrong P4 model.
Fix the constant TSC logic to cover all later P4 models. End at
INTEL_P4_CEDARMILL which accurately corresponds to the last P4 model.
Fixes: fadb6f569b10 ("x86/cpu/intel: Limit the non-architectural constant_tsc model checks")
Signed-off-by: Suchit Karunakaran <suchitkarunakaran(a)gmail.com>
Signed-off-by: Dave Hansen <dave.hansen(a)linux.intel.com>
Reviewed-by: Sohil Mehta <sohil.mehta(a)intel.com>
Cc:stable@vger.kernel.org
Link: https://lore.kernel.org/all/20250816065126.5000-1-suchitkarunakaran%40gmail…
---
arch/x86/kernel/cpu/intel.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 076eaa4..98ae4c3 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -262,7 +262,7 @@ static void early_init_intel(struct cpuinfo_x86 *c)
if (c->x86_power & (1 << 8)) {
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
- } else if ((c->x86_vfm >= INTEL_P4_PRESCOTT && c->x86_vfm <= INTEL_P4_WILLAMETTE) ||
+ } else if ((c->x86_vfm >= INTEL_P4_PRESCOTT && c->x86_vfm <= INTEL_P4_CEDARMILL) ||
(c->x86_vfm >= INTEL_CORE_YONAH && c->x86_vfm <= INTEL_IVYBRIDGE)) {
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
}
Introduce and use {pgd,p4d}_populate_kernel() in core MM code when
populating PGD and P4D entries for the kernel address space.
These helpers ensure proper synchronization of page tables when
updating the kernel portion of top-level page tables.
Until now, the kernel has relied on each architecture to handle
synchronization of top-level page tables in an ad-hoc manner.
For example, see commit 9b861528a801 ("x86-64, mem: Update all PGDs for
direct mapping and vmemmap mapping changes").
However, this approach has proven fragile for following reasons:
1) It is easy to forget to perform the necessary page table
synchronization when introducing new changes.
For instance, commit 4917f55b4ef9 ("mm/sparse-vmemmap: improve memory
savings for compound devmaps") overlooked the need to synchronize
page tables for the vmemmap area.
2) It is also easy to overlook that the vmemmap and direct mapping areas
must not be accessed before explicit page table synchronization.
For example, commit 8d400913c231 ("x86/vmemmap: handle unpopulated
sub-pmd ranges")) caused crashes by accessing the vmemmap area
before calling sync_global_pgds().
To address this, as suggested by Dave Hansen, introduce _kernel() variants
of the page table population helpers, which invoke architecture-specific
hooks to properly synchronize page tables. These are introduced in a new
header file, include/linux/pgalloc.h, so they can be called from common code.
They reuse existing infrastructure for vmalloc and ioremap.
Synchronization requirements are determined by ARCH_PAGE_TABLE_SYNC_MASK,
and the actual synchronization is performed by arch_sync_kernel_mappings().
This change currently targets only x86_64, so only PGD and P4D level
helpers are introduced. Currently, these helpers are no-ops since no
architecture sets PGTBL_{PGD,P4D}_MODIFIED in ARCH_PAGE_TABLE_SYNC_MASK.
In theory, PUD and PMD level helpers can be added later if needed by
other architectures. For now, 32-bit architectures (x86-32 and arm) only
handle PGTBL_PMD_MODIFIED, so p*d_populate_kernel() will never affect
them unless we introduce a PMD level helper.
Cc: <stable(a)vger.kernel.org>
Fixes: 8d400913c231 ("x86/vmemmap: handle unpopulated sub-pmd ranges")
Suggested-by: Dave Hansen <dave.hansen(a)linux.intel.com>
Acked-by: Kiryl Shutsemau <kas(a)kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt(a)kernel.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes(a)oracle.com>
Signed-off-by: Harry Yoo <harry.yoo(a)oracle.com>
---
include/linux/pgalloc.h | 24 ++++++++++++++++++++++++
include/linux/pgtable.h | 13 +++++++------
mm/kasan/init.c | 12 ++++++------
mm/percpu.c | 6 +++---
mm/sparse-vmemmap.c | 6 +++---
5 files changed, 43 insertions(+), 18 deletions(-)
create mode 100644 include/linux/pgalloc.h
diff --git a/include/linux/pgalloc.h b/include/linux/pgalloc.h
new file mode 100644
index 000000000000..290ab864320f
--- /dev/null
+++ b/include/linux/pgalloc.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_PGALLOC_H
+#define _LINUX_PGALLOC_H
+
+#include <linux/pgtable.h>
+#include <asm/pgalloc.h>
+
+static inline void pgd_populate_kernel(unsigned long addr, pgd_t *pgd,
+ p4d_t *p4d)
+{
+ pgd_populate(&init_mm, pgd, p4d);
+ if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_PGD_MODIFIED)
+ arch_sync_kernel_mappings(addr, addr);
+}
+
+static inline void p4d_populate_kernel(unsigned long addr, p4d_t *p4d,
+ pud_t *pud)
+{
+ p4d_populate(&init_mm, p4d, pud);
+ if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_P4D_MODIFIED)
+ arch_sync_kernel_mappings(addr, addr);
+}
+
+#endif /* _LINUX_PGALLOC_H */
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index ba699df6ef69..2b80fd456c8b 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1469,8 +1469,8 @@ static inline void modify_prot_commit_ptes(struct vm_area_struct *vma, unsigned
/*
* Architectures can set this mask to a combination of PGTBL_P?D_MODIFIED values
- * and let generic vmalloc and ioremap code know when arch_sync_kernel_mappings()
- * needs to be called.
+ * and let generic vmalloc, ioremap and page table update code know when
+ * arch_sync_kernel_mappings() needs to be called.
*/
#ifndef ARCH_PAGE_TABLE_SYNC_MASK
#define ARCH_PAGE_TABLE_SYNC_MASK 0
@@ -1954,10 +1954,11 @@ static inline bool arch_has_pfn_modify_check(void)
/*
* Page Table Modification bits for pgtbl_mod_mask.
*
- * These are used by the p?d_alloc_track*() set of functions an in the generic
- * vmalloc/ioremap code to track at which page-table levels entries have been
- * modified. Based on that the code can better decide when vmalloc and ioremap
- * mapping changes need to be synchronized to other page-tables in the system.
+ * These are used by the p?d_alloc_track*() and p*d_populate_kernel()
+ * functions in the generic vmalloc, ioremap and page table update code
+ * to track at which page-table levels entries have been modified.
+ * Based on that the code can better decide when page table changes need
+ * to be synchronized to other page-tables in the system.
*/
#define __PGTBL_PGD_MODIFIED 0
#define __PGTBL_P4D_MODIFIED 1
diff --git a/mm/kasan/init.c b/mm/kasan/init.c
index ced6b29fcf76..8fce3370c84e 100644
--- a/mm/kasan/init.c
+++ b/mm/kasan/init.c
@@ -13,9 +13,9 @@
#include <linux/mm.h>
#include <linux/pfn.h>
#include <linux/slab.h>
+#include <linux/pgalloc.h>
#include <asm/page.h>
-#include <asm/pgalloc.h>
#include "kasan.h"
@@ -191,7 +191,7 @@ static int __ref zero_p4d_populate(pgd_t *pgd, unsigned long addr,
pud_t *pud;
pmd_t *pmd;
- p4d_populate(&init_mm, p4d,
+ p4d_populate_kernel(addr, p4d,
lm_alias(kasan_early_shadow_pud));
pud = pud_offset(p4d, addr);
pud_populate(&init_mm, pud,
@@ -212,7 +212,7 @@ static int __ref zero_p4d_populate(pgd_t *pgd, unsigned long addr,
} else {
p = early_alloc(PAGE_SIZE, NUMA_NO_NODE);
pud_init(p);
- p4d_populate(&init_mm, p4d, p);
+ p4d_populate_kernel(addr, p4d, p);
}
}
zero_pud_populate(p4d, addr, next);
@@ -251,10 +251,10 @@ int __ref kasan_populate_early_shadow(const void *shadow_start,
* puds,pmds, so pgd_populate(), pud_populate()
* is noops.
*/
- pgd_populate(&init_mm, pgd,
+ pgd_populate_kernel(addr, pgd,
lm_alias(kasan_early_shadow_p4d));
p4d = p4d_offset(pgd, addr);
- p4d_populate(&init_mm, p4d,
+ p4d_populate_kernel(addr, p4d,
lm_alias(kasan_early_shadow_pud));
pud = pud_offset(p4d, addr);
pud_populate(&init_mm, pud,
@@ -273,7 +273,7 @@ int __ref kasan_populate_early_shadow(const void *shadow_start,
if (!p)
return -ENOMEM;
} else {
- pgd_populate(&init_mm, pgd,
+ pgd_populate_kernel(addr, pgd,
early_alloc(PAGE_SIZE, NUMA_NO_NODE));
}
}
diff --git a/mm/percpu.c b/mm/percpu.c
index d9cbaee92b60..a56f35dcc417 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -3108,7 +3108,7 @@ int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
#endif /* BUILD_EMBED_FIRST_CHUNK */
#ifdef BUILD_PAGE_FIRST_CHUNK
-#include <asm/pgalloc.h>
+#include <linux/pgalloc.h>
#ifndef P4D_TABLE_SIZE
#define P4D_TABLE_SIZE PAGE_SIZE
@@ -3134,13 +3134,13 @@ void __init __weak pcpu_populate_pte(unsigned long addr)
if (pgd_none(*pgd)) {
p4d = memblock_alloc_or_panic(P4D_TABLE_SIZE, P4D_TABLE_SIZE);
- pgd_populate(&init_mm, pgd, p4d);
+ pgd_populate_kernel(addr, pgd, p4d);
}
p4d = p4d_offset(pgd, addr);
if (p4d_none(*p4d)) {
pud = memblock_alloc_or_panic(PUD_TABLE_SIZE, PUD_TABLE_SIZE);
- p4d_populate(&init_mm, p4d, pud);
+ p4d_populate_kernel(addr, p4d, pud);
}
pud = pud_offset(p4d, addr);
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 41aa0493eb03..dbd8daccade2 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -27,9 +27,9 @@
#include <linux/spinlock.h>
#include <linux/vmalloc.h>
#include <linux/sched.h>
+#include <linux/pgalloc.h>
#include <asm/dma.h>
-#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include "hugetlb_vmemmap.h"
@@ -229,7 +229,7 @@ p4d_t * __meminit vmemmap_p4d_populate(pgd_t *pgd, unsigned long addr, int node)
if (!p)
return NULL;
pud_init(p);
- p4d_populate(&init_mm, p4d, p);
+ p4d_populate_kernel(addr, p4d, p);
}
return p4d;
}
@@ -241,7 +241,7 @@ pgd_t * __meminit vmemmap_pgd_populate(unsigned long addr, int node)
void *p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
if (!p)
return NULL;
- pgd_populate(&init_mm, pgd, p);
+ pgd_populate_kernel(addr, pgd, p);
}
return pgd;
}
--
2.43.0
The patch titled
Subject: arm64: kexec: Initialize kexec_buf struct in image_load()
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
arm64-kexec-initialize-kexec_buf-struct-in-image_load.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patche…
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Breno Leitao <leitao(a)debian.org>
Subject: arm64: kexec: Initialize kexec_buf struct in image_load()
Date: Tue, 26 Aug 2025 05:08:51 -0700
The kexec_buf structure was previously declared without initialization in
image_load(). This led to a UBSAN warning when the structure was expanded
and uninitialized fields were accessed [1].
Zero-initializing kexec_buf at declaration ensures all fields are cleanly
set, preventing future instances of uninitialized memory being used.
Fixes this UBSAN warning:
[ 32.362488] UBSAN: invalid-load in ./include/linux/kexec.h:210:10
[ 32.362649] load of value 252 is not a valid value for type '_Bool'
Andrew Morton suggested that this function is only called 3x a week[2],
thus, the memset() cost is inexpensive.
Link: https://lore.kernel.org/all/oninomspajhxp4omtdapxnckxydbk2nzmrix7rggmpukpnz… [1]
Link: https://lore.kernel.org/all/20250825180531.94bfb86a26a43127c0a1296f@linux-f… [2]
Link: https://lkml.kernel.org/r/20250826-akpm-v1-1-3c831f0e3799@debian.org
Fixes: bf454ec31add ("kexec_file: allow to place kexec_buf randomly")
Signed-off-by: Breno Leitao <leitao(a)debian.org>
Suggested-by: Andrew Morton <akpm(a)linux-foundation.org>
Cc: Mark Rutland <mark.rutland(a)arm.com>
Cc: Baoquan He <bhe(a)redhat.com>
Cc: Coiby Xu <coxu(a)redhat.com>
Cc: "Daniel P. Berrange" <berrange(a)redhat.com>
Cc: Dave Hansen <dave.hansen(a)intel.com>
Cc: Dave Young <dyoung(a)redhat.com>
Cc: Kairui Song <ryncsn(a)gmail.com>
Cc: Liu Pingfan <kernelfans(a)gmail.com>
Cc: Milan Broz <gmazyland(a)gmail.com>
Cc: Ondrej Kozina <okozina(a)redhat.com>
Cc: Vitaly Kuznetsov <vkuznets(a)redhat.com>
Cc: <stable(a)vger.kernel.org>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
---
arch/arm64/kernel/kexec_image.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/arm64/kernel/kexec_image.c~arm64-kexec-initialize-kexec_buf-struct-in-image_load
+++ a/arch/arm64/kernel/kexec_image.c
@@ -41,7 +41,7 @@ static void *image_load(struct kimage *i
struct arm64_image_header *h;
u64 flags, value;
bool be_image, be_kernel;
- struct kexec_buf kbuf;
+ struct kexec_buf kbuf = {};
unsigned long text_offset, kernel_segment_number;
struct kexec_segment *kernel_segment;
int ret;
_
Patches currently in -mm which might be from leitao(a)debian.org are
arm64-kexec-initialize-kexec_buf-struct-in-image_load.patch
The quilt patch titled
Subject: kexec/arm64: initialize the random field of kbuf to zero in the image loader
has been removed from the -mm tree. Its filename was
kexec-arm64-initialize-the-random-field-of-kbuf-to-zero-in-the-image-loader.patch
This patch was dropped because an updated version will be issued
------------------------------------------------------
From: Breno Leitao <leitao(a)debian.org>
Subject: kexec/arm64: initialize the random field of kbuf to zero in the image loader
Date: Thu Aug 21 04:11:21 2025 -0700
Add an explicit initialization for the random member of the kbuf structure
within the image_load function in arch/arm64/kernel/kexec_image.c.
Setting kbuf.random to zero ensures a deterministic and clean starting
state for the buffer used during kernel image loading, avoiding this UBSAN
issue later, when kbuf.random is read.
[ 32.362488] UBSAN: invalid-load in ./include/linux/kexec.h:210:10
[ 32.362649] load of value 252 is not a valid value for type '_Bool'
Link: https://lkml.kernel.org/r/oninomspajhxp4omtdapxnckxydbk2nzmrix7rggmpukpnzad…
Fixes: bf454ec31add ("kexec_file: allow to place kexec_buf randomly")
Signed-off-by: Breno Leitao <leitao(a)debian.org>
Cc: Mark Rutland <mark.rutland(a)arm.com>
Cc: Baoquan He <bhe(a)redhat.com>
Cc: Coiby Xu <coxu(a)redhat.com>
Cc: "Daniel P. Berrange" <berrange(a)redhat.com>
Cc: Dave Hansen <dave.hansen(a)intel.com>
Cc: Dave Young <dyoung(a)redhat.com>
Cc: Kairui Song <ryncsn(a)gmail.com>
Cc: Liu Pingfan <kernelfans(a)gmail.com>
Cc: Milan Broz <gmazyland(a)gmail.com>
Cc: Ondrej Kozina <okozina(a)redhat.com>
Cc: Vitaly Kuznetsov <vkuznets(a)redhat.com>
Cc: <stable(a)vger.kernel.org>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
---
arch/arm64/kernel/kexec_image.c | 1 +
1 file changed, 1 insertion(+)
--- a/arch/arm64/kernel/kexec_image.c~kexec-arm64-initialize-the-random-field-of-kbuf-to-zero-in-the-image-loader
+++ a/arch/arm64/kernel/kexec_image.c
@@ -76,6 +76,7 @@ static void *image_load(struct kimage *i
kbuf.buf_min = 0;
kbuf.buf_max = ULONG_MAX;
kbuf.top_down = false;
+ kbuf.random = 0;
kbuf.buffer = kernel;
kbuf.bufsz = kernel_len;
_
Patches currently in -mm which might be from leitao(a)debian.org are
There are some AA deadlock issues in kmemleak, similar to the situation
reported by Breno [1]. The deadlock path is as follows:
mem_pool_alloc()
-> raw_spin_lock_irqsave(&kmemleak_lock, flags);
-> pr_warn()
-> netconsole subsystem
-> netpoll
-> __alloc_skb
-> __create_object
-> raw_spin_lock_irqsave(&kmemleak_lock, flags);
To solve this problem, switch to printk_safe mode before printing warning
message, this will redirect all printk()-s to a special per-CPU buffer,
which will be flushed later from a safe context (irq work), and this
deadlock problem can be avoided. The proper API to use should be
printk_deferred_enter()/printk_deferred_exit() [2]. Another way is to
place the warn print after kmemleak is released.
[1]
https://lore.kernel.org/all/20250731-kmemleak_lock-v1-1-728fd470198f@debian…
[2]
https://lore.kernel.org/all/5ca375cd-4a20-4807-b897-68b289626550@redhat.com/
====================
Signed-off-by: Gu Bowen <gubowen5(a)huawei.com>
---
mm/kmemleak.c | 27 ++++++++++++++++++++-------
1 file changed, 20 insertions(+), 7 deletions(-)
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 84265983f239..1ac56ceb29b6 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -437,9 +437,15 @@ static struct kmemleak_object *__lookup_object(unsigned long ptr, int alias,
else if (untagged_objp == untagged_ptr || alias)
return object;
else {
+ /*
+ * Printk deferring due to the kmemleak_lock held.
+ * This is done to avoid deadlock.
+ */
+ printk_deferred_enter();
kmemleak_warn("Found object by alias at 0x%08lx\n",
ptr);
dump_object_info(object);
+ printk_deferred_exit();
break;
}
}
@@ -736,6 +742,11 @@ static int __link_object(struct kmemleak_object *object, unsigned long ptr,
else if (untagged_objp + parent->size <= untagged_ptr)
link = &parent->rb_node.rb_right;
else {
+ /*
+ * Printk deferring due to the kmemleak_lock held.
+ * This is done to avoid deadlock.
+ */
+ printk_deferred_enter();
kmemleak_stop("Cannot insert 0x%lx into the object search tree (overlaps existing)\n",
ptr);
/*
@@ -743,6 +754,7 @@ static int __link_object(struct kmemleak_object *object, unsigned long ptr,
* be freed while the kmemleak_lock is held.
*/
dump_object_info(parent);
+ printk_deferred_exit();
return -EEXIST;
}
}
@@ -856,13 +868,8 @@ static void delete_object_part(unsigned long ptr, size_t size,
raw_spin_lock_irqsave(&kmemleak_lock, flags);
object = __find_and_remove_object(ptr, 1, objflags);
- if (!object) {
-#ifdef DEBUG
- kmemleak_warn("Partially freeing unknown object at 0x%08lx (size %zu)\n",
- ptr, size);
-#endif
+ if (!object)
goto unlock;
- }
/*
* Create one or two objects that may result from the memory block
@@ -882,8 +889,14 @@ static void delete_object_part(unsigned long ptr, size_t size,
unlock:
raw_spin_unlock_irqrestore(&kmemleak_lock, flags);
- if (object)
+ if (object) {
__delete_object(object);
+ } else {
+#ifdef DEBUG
+ kmemleak_warn("Partially freeing unknown object at 0x%08lx (size %zu)\n",
+ ptr, size);
+#endif
+ }
out:
if (object_l)
--
2.43.0
[BUG]
With 64K page size (aarch64 with 64K page size config) and 4K btrfs
block size, the following workload can easily lead to a corrupted read:
mkfs.btrfs -f -s 4k $dev > /dev/null
mount -o compress $dev $mnt
xfs_io -f -c "pwrite -S 0xff 0 64k" $mnt/base > /dev/null
echo "correct result:"
od -Ad -t x1 $mnt/base
xfs_io -f -c "reflink $mnt/base 32k 0 32k" \
-c "reflink $mnt/base 0 32k 32k" \
-c "pwrite -S 0xff 60k 4k" $mnt/new > /dev/null
echo "incorrect result:"
od -Ad -t x1 $mnt/new
umount $mnt
This shows the following result:
correct result:
0000000 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
*
0065536
incorrect result:
0000000 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
*
0032768 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
*
0061440 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
*
0065536
Notice the zero in the range [32K, 60K), which is incorrect.
[CAUSE]
With extra trace printk, it shows the following events during od:
(some unrelated info removed like CPU and context)
od-3457 btrfs_do_readpage: enter r/i=5/258 folio=0(65536) prev_em_start=0000000000000000
The "r/i" is indicating the root and inode number. In our case the file
"new" is using ino 258 from fs tree (root 5).
Here notice the @prev_em_start pointer is NULL. This means the
btrfs_do_readpage() is called from btrfs_read_folio(), not from
btrfs_readahead().
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=0 got em start=0 len=32768
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=4096 got em start=0 len=32768
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=8192 got em start=0 len=32768
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=12288 got em start=0 len=32768
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=16384 got em start=0 len=32768
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=20480 got em start=0 len=32768
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=24576 got em start=0 len=32768
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=28672 got em start=0 len=32768
These above 32K blocks will be read from the first half of the
compressed data extent.
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=32768 got em start=32768 len=32768
Note here there is no btrfs_submit_compressed_read() call. Which is
incorrect now.
Although both extent maps at 0 and 32K are pointing to the same compressed
data, their offsets are different thus can not be merged into the same
read.
So this means the compressed data read merge check is doing something
wrong.
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=36864 got em start=32768 len=32768
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=40960 got em start=32768 len=32768
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=45056 got em start=32768 len=32768
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=49152 got em start=32768 len=32768
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=53248 got em start=32768 len=32768
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=57344 got em start=32768 len=32768
od-3457 btrfs_do_readpage: r/i=5/258 folio=0(65536) cur=61440 skip uptodate
od-3457 btrfs_submit_compressed_read: cb orig_bio: file off=0 len=61440
The function btrfs_submit_compressed_read() is only called at the end of
folio read. The compressed bio will only have an extent map of range [0,
32K), but the original bio passed in is for the whole 64K folio.
This will cause the decompression part to only fill the first 32K,
leaving the rest untouched (aka, filled with zero).
This incorrect compressed read merge leads to the above data corruption.
There were similar problems that happened in the past, commit 808f80b46790
("Btrfs: update fix for read corruption of compressed and shared
extents") is doing pretty much the same fix for readahead.
But that's back to 2015, where btrfs still only supports bs (block size)
== ps (page size) cases.
This means btrfs_do_readpage() only needs to handle a folio which
contains exactly one block.
Only btrfs_readahead() can lead to a read covering multiple blocks.
Thus only btrfs_readahead() passes a non-NULL @prev_em_start pointer.
With v5.15 kernel btrfs introduced bs < ps support. This breaks the above
assumption that a folio can only contain one block.
Now btrfs_read_folio() can also read multiple blocks in one go.
But btrfs_read_folio() doesn't pass a @prev_em_start pointer, thus the
existing bio force submission check will never be triggered.
In theory, this can also happen for btrfs with large folios, but since
large folio is still experimental, we don't need to bother it, thus only
bs < ps support is affected for now.
[FIX]
Instead of passing @prev_em_start to do the proper compressed extent
check, introduce one new member, btrfs_bio_ctrl::last_em_start, so that
the existing bio force submission logic will always be triggered.
CC: stable(a)vger.kernel.org # 5.15+
Reviewed-by: Filipe Manana <fdmanana(a)suse.com>
Signed-off-by: Qu Wenruo <wqu(a)suse.com>
Signed-off-by: David Sterba <dsterba(a)suse.com>
---
Changelog:
v4:
- Minor grammar fixes
- Update the subject to reflect the bug better
This is the merged version inside for-next branch.
However for people who are not following our development branch but
still want to verify the incoming fstests test case, we need this fix
to be publicly avaiable. Newer minor changes will only be done inside
the development branch.
v3:
- Use a single btrfs_bio_ctrl::last_em_start
Since the existing prev_em_start is using U64_MAX as the initial value
to indicate no em hit yet, we can use the same logic, which saves
another 8 bytes from btrfs_bio_ctrl.
- Update the reproducer
Previously I failed to reproduce using a minimal workload.
As regular read from od/md5sum always trigger readahead thus not
hitting the @prev_em_start == NULL path.
Will send out a fstest case for it using the minimal reproducer.
But it will still need a 16K/64K page sized system to reproduce.
Fix the problem by doing an block aligned write into the folio, so
that the folio will be partially dirty and not go through the
readahead path.
- Update the analyze
This includes the trace events of the minimal reproducer, and
mentioning of previous similar fixes and why they do not work for
subpage cases.
- Update the CC tag
Since it's only affecting bs < ps cases (for non-experimental builds),
only need to fix kernels with subpage btrfs supports.
v2:
- Only save extent_map::start/len to save memory for btrfs_bio_ctrl
It's using on-stack memory which is very limited inside the kernel.
- Remove the commit message mentioning of clearing last saved em
Since we're using em::start/len, there is no need to clear them.
Either we hit the same em::start/len, meaning hitting the same extent
map, or we hit a different em, which will have a different start/len.
---
fs/btrfs/extent_io.c | 40 ++++++++++++++++++++++++++++++----------
1 file changed, 30 insertions(+), 10 deletions(-)
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 426a6791a0b2..ca7174fa0240 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -131,6 +131,24 @@ struct btrfs_bio_ctrl {
*/
unsigned long submit_bitmap;
struct readahead_control *ractl;
+
+ /*
+ * The start offset of the last used extent map by a read operation.
+ *
+ * This is for proper compressed read merge.
+ * U64_MAX means we are starting the read and have made no progress yet.
+ *
+ * The current btrfs_bio_is_contig() only uses disk_bytenr as
+ * the condition to check if the read can be merged with previous
+ * bio, which is not correct. E.g. two file extents pointing to the
+ * same extent but with different offset.
+ *
+ * So here we need to do extra checks to only merge reads that are
+ * covered by the same extent map.
+ * Just extent_map::start will be enough, as they are unique
+ * inside the same inode.
+ */
+ u64 last_em_start;
};
/*
@@ -965,7 +983,7 @@ static void btrfs_readahead_expand(struct readahead_control *ractl,
* return 0 on success, otherwise return error
*/
static int btrfs_do_readpage(struct folio *folio, struct extent_map **em_cached,
- struct btrfs_bio_ctrl *bio_ctrl, u64 *prev_em_start)
+ struct btrfs_bio_ctrl *bio_ctrl)
{
struct inode *inode = folio->mapping->host;
struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
@@ -1076,12 +1094,11 @@ static int btrfs_do_readpage(struct folio *folio, struct extent_map **em_cached,
* non-optimal behavior (submitting 2 bios for the same extent).
*/
if (compress_type != BTRFS_COMPRESS_NONE &&
- prev_em_start && *prev_em_start != (u64)-1 &&
- *prev_em_start != em->start)
+ bio_ctrl->last_em_start != U64_MAX &&
+ bio_ctrl->last_em_start != em->start)
force_bio_submit = true;
- if (prev_em_start)
- *prev_em_start = em->start;
+ bio_ctrl->last_em_start = em->start;
em_gen = em->generation;
btrfs_free_extent_map(em);
@@ -1296,12 +1313,15 @@ int btrfs_read_folio(struct file *file, struct folio *folio)
const u64 start = folio_pos(folio);
const u64 end = start + folio_size(folio) - 1;
struct extent_state *cached_state = NULL;
- struct btrfs_bio_ctrl bio_ctrl = { .opf = REQ_OP_READ };
+ struct btrfs_bio_ctrl bio_ctrl = {
+ .opf = REQ_OP_READ,
+ .last_em_start = U64_MAX,
+ };
struct extent_map *em_cached = NULL;
int ret;
lock_extents_for_read(inode, start, end, &cached_state);
- ret = btrfs_do_readpage(folio, &em_cached, &bio_ctrl, NULL);
+ ret = btrfs_do_readpage(folio, &em_cached, &bio_ctrl);
btrfs_unlock_extent(&inode->io_tree, start, end, &cached_state);
btrfs_free_extent_map(em_cached);
@@ -2641,7 +2661,8 @@ void btrfs_readahead(struct readahead_control *rac)
{
struct btrfs_bio_ctrl bio_ctrl = {
.opf = REQ_OP_READ | REQ_RAHEAD,
- .ractl = rac
+ .ractl = rac,
+ .last_em_start = U64_MAX,
};
struct folio *folio;
struct btrfs_inode *inode = BTRFS_I(rac->mapping->host);
@@ -2649,12 +2670,11 @@ void btrfs_readahead(struct readahead_control *rac)
const u64 end = start + readahead_length(rac) - 1;
struct extent_state *cached_state = NULL;
struct extent_map *em_cached = NULL;
- u64 prev_em_start = (u64)-1;
lock_extents_for_read(inode, start, end, &cached_state);
while ((folio = readahead_folio(rac)) != NULL)
- btrfs_do_readpage(folio, &em_cached, &bio_ctrl, &prev_em_start);
+ btrfs_do_readpage(folio, &em_cached, &bio_ctrl);
btrfs_unlock_extent(&inode->io_tree, start, end, &cached_state);
--
2.50.1