arch/arm/mm/fault-armv.c | 40 ++++++++++++++++++++++++++++------------ 1 file changed, 28 insertions(+), 12 deletions(-)
When update_mmu_cache_range() is called by update_mmu_cache(), the vmf
parameter is NULL, which will cause a NULL pointer dereference issue in
adjust_pte():
Unable to handle kernel NULL pointer dereference at virtual address 00000030 when read
Hardware name: Atmel AT91SAM9
PC is at update_mmu_cache_range+0x1e0/0x278
LR is at pte_offset_map_rw_nolock+0x18/0x2c
Call trace:
update_mmu_cache_range from remove_migration_pte+0x29c/0x2ec
remove_migration_pte from rmap_walk_file+0xcc/0x130
rmap_walk_file from remove_migration_ptes+0x90/0xa4
remove_migration_ptes from migrate_pages_batch+0x6d4/0x858
migrate_pages_batch from migrate_pages+0x188/0x488
migrate_pages from compact_zone+0x56c/0x954
compact_zone from compact_node+0x90/0xf0
compact_node from kcompactd+0x1d4/0x204
kcompactd from kthread+0x120/0x12c
kthread from ret_from_fork+0x14/0x38
Exception stack(0xc0d8bfb0 to 0xc0d8bff8)
To fix it, do not rely on whether 'ptl' is equal to decide whether to hold
the pte lock, but decide it by whether CONFIG_SPLIT_PTE_PTLOCKS is
enabled. In addition, if two vmas map to the same PTE page, there is no
need to hold the pte lock again, otherwise a deadlock will occur. Just add
the need_lock parameter to let adjust_pte() know this information.
Reported-by: Ezra Buehler <ezra@easyb.ch>
Closes: https://lore.kernel.org/lkml/CAM1KZSmZ2T_riHvay+7cKEFxoPgeVpHkVFTzVVEQ1BO0cLkHEQ@mail.gmail.com/
Fixes: fc9c45b71f43 ("arm: adjust_pte() use pte_offset_map_rw_nolock()")
Cc: stable@vger.kernel.org
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
arch/arm/mm/fault-armv.c | 40 ++++++++++++++++++++++++++++------------
1 file changed, 28 insertions(+), 12 deletions(-)
diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
index 2bec87c3327d2..3627bf0957c75 100644
--- a/arch/arm/mm/fault-armv.c
+++ b/arch/arm/mm/fault-armv.c
@@ -62,7 +62,7 @@ static int do_adjust_pte(struct vm_area_struct *vma, unsigned long address,
}
static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
- unsigned long pfn, struct vm_fault *vmf)
+ unsigned long pfn, bool need_lock)
{
spinlock_t *ptl;
pgd_t *pgd;
@@ -99,12 +99,11 @@ static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
if (!pte)
return 0;
- /*
- * If we are using split PTE locks, then we need to take the page
- * lock here. Otherwise we are using shared mm->page_table_lock
- * which is already locked, thus cannot take it.
- */
- if (ptl != vmf->ptl) {
+ if (need_lock) {
+ /*
+ * Use nested version here to indicate that we are already
+ * holding one similar spinlock.
+ */
spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pmd)))) {
pte_unmap_unlock(pte, ptl);
@@ -114,7 +113,7 @@ static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
ret = do_adjust_pte(vma, address, pfn, pte);
- if (ptl != vmf->ptl)
+ if (need_lock)
spin_unlock(ptl);
pte_unmap(pte);
@@ -123,16 +122,17 @@ static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
static void
make_coherent(struct address_space *mapping, struct vm_area_struct *vma,
- unsigned long addr, pte_t *ptep, unsigned long pfn,
- struct vm_fault *vmf)
+ unsigned long addr, pte_t *ptep, unsigned long pfn)
{
struct mm_struct *mm = vma->vm_mm;
struct vm_area_struct *mpnt;
unsigned long offset;
+ unsigned long start;
pgoff_t pgoff;
int aliases = 0;
pgoff = vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT);
+ start = ALIGN_DOWN(addr, PMD_SIZE);
/*
* If we have any shared mappings that are in the same mm
@@ -141,6 +141,14 @@ make_coherent(struct address_space *mapping, struct vm_area_struct *vma,
*/
flush_dcache_mmap_lock(mapping);
vma_interval_tree_foreach(mpnt, &mapping->i_mmap, pgoff, pgoff) {
+ unsigned long mpnt_addr;
+ /*
+ * If we are using split PTE locks, then we need to take the pte
+ * lock. Otherwise we are using shared mm->page_table_lock which
+ * is already locked, thus cannot take it.
+ */
+ bool need_lock = IS_ENABLED(CONFIG_SPLIT_PTE_PTLOCKS);
+
/*
* If this VMA is not in our MM, we can ignore it.
* Note that we intentionally mask out the VMA
@@ -151,7 +159,15 @@ make_coherent(struct address_space *mapping, struct vm_area_struct *vma,
if (!(mpnt->vm_flags & VM_MAYSHARE))
continue;
offset = (pgoff - mpnt->vm_pgoff) << PAGE_SHIFT;
- aliases += adjust_pte(mpnt, mpnt->vm_start + offset, pfn, vmf);
+ mpnt_addr = mpnt->vm_start + offset;
+ /*
+ * If mpnt_addr and addr are mapped to the same PTE page, there
+ * is no need to hold the pte lock again, otherwise a deadlock
+ * will occur.
+ */
+ if (mpnt_addr >= start && mpnt_addr - start < PMD_SIZE)
+ need_lock = false;
+ aliases += adjust_pte(mpnt, mpnt_addr, pfn, need_lock);
}
flush_dcache_mmap_unlock(mapping);
if (aliases)
@@ -194,7 +210,7 @@ void update_mmu_cache_range(struct vm_fault *vmf, struct vm_area_struct *vma,
__flush_dcache_folio(mapping, folio);
if (mapping) {
if (cache_is_vivt())
- make_coherent(mapping, vma, addr, ptep, pfn, vmf);
+ make_coherent(mapping, vma, addr, ptep, pfn);
else if (vma->vm_flags & VM_EXEC)
__flush_icache_all();
}
--
2.20.1On 12.02.25 07:40, Qi Zheng wrote:
> When update_mmu_cache_range() is called by update_mmu_cache(), the vmf
> parameter is NULL, which will cause a NULL pointer dereference issue in
> adjust_pte():
>
> Unable to handle kernel NULL pointer dereference at virtual address 00000030 when read
> Hardware name: Atmel AT91SAM9
> PC is at update_mmu_cache_range+0x1e0/0x278
> LR is at pte_offset_map_rw_nolock+0x18/0x2c
> Call trace:
> update_mmu_cache_range from remove_migration_pte+0x29c/0x2ec
> remove_migration_pte from rmap_walk_file+0xcc/0x130
> rmap_walk_file from remove_migration_ptes+0x90/0xa4
> remove_migration_ptes from migrate_pages_batch+0x6d4/0x858
> migrate_pages_batch from migrate_pages+0x188/0x488
> migrate_pages from compact_zone+0x56c/0x954
> compact_zone from compact_node+0x90/0xf0
> compact_node from kcompactd+0x1d4/0x204
> kcompactd from kthread+0x120/0x12c
> kthread from ret_from_fork+0x14/0x38
> Exception stack(0xc0d8bfb0 to 0xc0d8bff8)
>
> To fix it, do not rely on whether 'ptl' is equal to decide whether to hold
> the pte lock, but decide it by whether CONFIG_SPLIT_PTE_PTLOCKS is
> enabled. In addition, if two vmas map to the same PTE page, there is no
> need to hold the pte lock again, otherwise a deadlock will occur. Just add
> the need_lock parameter to let adjust_pte() know this information.
>
> Reported-by: Ezra Buehler <ezra@easyb.ch>
> Closes: https://lore.kernel.org/lkml/CAM1KZSmZ2T_riHvay+7cKEFxoPgeVpHkVFTzVVEQ1BO0cLkHEQ@mail.gmail.com/
> Fixes: fc9c45b71f43 ("arm: adjust_pte() use pte_offset_map_rw_nolock()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
> arch/arm/mm/fault-armv.c | 40 ++++++++++++++++++++++++++++------------
> 1 file changed, 28 insertions(+), 12 deletions(-)
>
> diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
> index 2bec87c3327d2..3627bf0957c75 100644
> --- a/arch/arm/mm/fault-armv.c
> +++ b/arch/arm/mm/fault-armv.c
> @@ -62,7 +62,7 @@ static int do_adjust_pte(struct vm_area_struct *vma, unsigned long address,
> }
>
> static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
> - unsigned long pfn, struct vm_fault *vmf)
> + unsigned long pfn, bool need_lock)
> {
> spinlock_t *ptl;
> pgd_t *pgd;
> @@ -99,12 +99,11 @@ static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
> if (!pte)
> return 0;
>
> - /*
> - * If we are using split PTE locks, then we need to take the page
> - * lock here. Otherwise we are using shared mm->page_table_lock
> - * which is already locked, thus cannot take it.
> - */
> - if (ptl != vmf->ptl) {
> + if (need_lock) {
> + /*
> + * Use nested version here to indicate that we are already
> + * holding one similar spinlock.
> + */
> spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
> if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pmd)))) {
> pte_unmap_unlock(pte, ptl);
> @@ -114,7 +113,7 @@ static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
>
> ret = do_adjust_pte(vma, address, pfn, pte);
>
> - if (ptl != vmf->ptl)
> + if (need_lock)
> spin_unlock(ptl);
> pte_unmap(pte);
>
> @@ -123,16 +122,17 @@ static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
>
> static void
> make_coherent(struct address_space *mapping, struct vm_area_struct *vma,
> - unsigned long addr, pte_t *ptep, unsigned long pfn,
> - struct vm_fault *vmf)
> + unsigned long addr, pte_t *ptep, unsigned long pfn)
> {
> struct mm_struct *mm = vma->vm_mm;
> struct vm_area_struct *mpnt;
> unsigned long offset;
> + unsigned long start;
> pgoff_t pgoff;
> int aliases = 0;
>
> pgoff = vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT);
> + start = ALIGN_DOWN(addr, PMD_SIZE);
I assume you can come up with a better name than "start" :)
aligned_addr ... pmd_start_addr ...
Maybe simply
pmd_start_addr = ALIGN_DOWN(addr, PMD_SIZE);
pmd_end_addr = addr + PMD_SIZE;
Then the comparison below also becomes easier to read.
>
> /*
> * If we have any shared mappings that are in the same mm
> @@ -141,6 +141,14 @@ make_coherent(struct address_space *mapping, struct vm_area_struct *vma,
> */
> flush_dcache_mmap_lock(mapping);
> vma_interval_tree_foreach(mpnt, &mapping->i_mmap, pgoff, pgoff) {
> + unsigned long mpnt_addr;
> + /*
> + * If we are using split PTE locks, then we need to take the pte
> + * lock. Otherwise we are using shared mm->page_table_lock which
> + * is already locked, thus cannot take it.
> + */
> + bool need_lock = IS_ENABLED(CONFIG_SPLIT_PTE_PTLOCKS);
Nit: move "unsigned long mpnt_addr;" below this longer variable+init.
> +
> /*
> * If this VMA is not in our MM, we can ignore it.
> * Note that we intentionally mask out the VMA
> @@ -151,7 +159,15 @@ make_coherent(struct address_space *mapping, struct vm_area_struct *vma,
> if (!(mpnt->vm_flags & VM_MAYSHARE))
> continue;
> offset = (pgoff - mpnt->vm_pgoff) << PAGE_SHIFT;
> - aliases += adjust_pte(mpnt, mpnt->vm_start + offset, pfn, vmf);
> + mpnt_addr = mpnt->vm_start + offset;
> + /*
> + * If mpnt_addr and addr are mapped to the same PTE page, there
> + * is no need to hold the pte lock again, otherwise a deadlock
> + * will occur.
/*
* Avoid deadlocks by not grabbing the PTE lock if we already hold the
* PTE lock of this PTE table in the caller.
*/
?
> + */
> + if (mpnt_addr >= start && mpnt_addr - start < PMD_SIZE)
> + need_lock = false;
--
Cheers,
David / dhildenb
On 2025/2/12 16:20, David Hildenbrand wrote:
> On 12.02.25 07:40, Qi Zheng wrote:
>> When update_mmu_cache_range() is called by update_mmu_cache(), the vmf
>> parameter is NULL, which will cause a NULL pointer dereference issue in
>> adjust_pte():
>>
>> Unable to handle kernel NULL pointer dereference at virtual address
>> 00000030 when read
>> Hardware name: Atmel AT91SAM9
>> PC is at update_mmu_cache_range+0x1e0/0x278
>> LR is at pte_offset_map_rw_nolock+0x18/0x2c
>> Call trace:
>> update_mmu_cache_range from remove_migration_pte+0x29c/0x2ec
>> remove_migration_pte from rmap_walk_file+0xcc/0x130
>> rmap_walk_file from remove_migration_ptes+0x90/0xa4
>> remove_migration_ptes from migrate_pages_batch+0x6d4/0x858
>> migrate_pages_batch from migrate_pages+0x188/0x488
>> migrate_pages from compact_zone+0x56c/0x954
>> compact_zone from compact_node+0x90/0xf0
>> compact_node from kcompactd+0x1d4/0x204
>> kcompactd from kthread+0x120/0x12c
>> kthread from ret_from_fork+0x14/0x38
>> Exception stack(0xc0d8bfb0 to 0xc0d8bff8)
>>
>> To fix it, do not rely on whether 'ptl' is equal to decide whether to
>> hold
>> the pte lock, but decide it by whether CONFIG_SPLIT_PTE_PTLOCKS is
>> enabled. In addition, if two vmas map to the same PTE page, there is no
>> need to hold the pte lock again, otherwise a deadlock will occur. Just
>> add
>> the need_lock parameter to let adjust_pte() know this information.
>>
>> Reported-by: Ezra Buehler <ezra@easyb.ch>
>> Closes:
>> https://lore.kernel.org/lkml/CAM1KZSmZ2T_riHvay+7cKEFxoPgeVpHkVFTzVVEQ1BO0cLkHEQ@mail.gmail.com/
>> Fixes: fc9c45b71f43 ("arm: adjust_pte() use pte_offset_map_rw_nolock()")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> ---
>> arch/arm/mm/fault-armv.c | 40 ++++++++++++++++++++++++++++------------
>> 1 file changed, 28 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
>> index 2bec87c3327d2..3627bf0957c75 100644
>> --- a/arch/arm/mm/fault-armv.c
>> +++ b/arch/arm/mm/fault-armv.c
>> @@ -62,7 +62,7 @@ static int do_adjust_pte(struct vm_area_struct *vma,
>> unsigned long address,
>> }
>> static int adjust_pte(struct vm_area_struct *vma, unsigned long
>> address,
>> - unsigned long pfn, struct vm_fault *vmf)
>> + unsigned long pfn, bool need_lock)
>> {
>> spinlock_t *ptl;
>> pgd_t *pgd;
>> @@ -99,12 +99,11 @@ static int adjust_pte(struct vm_area_struct *vma,
>> unsigned long address,
>> if (!pte)
>> return 0;
>> - /*
>> - * If we are using split PTE locks, then we need to take the page
>> - * lock here. Otherwise we are using shared mm->page_table_lock
>> - * which is already locked, thus cannot take it.
>> - */
>> - if (ptl != vmf->ptl) {
>> + if (need_lock) {
>> + /*
>> + * Use nested version here to indicate that we are already
>> + * holding one similar spinlock.
>> + */
>> spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
>> if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pmd)))) {
>> pte_unmap_unlock(pte, ptl);
>> @@ -114,7 +113,7 @@ static int adjust_pte(struct vm_area_struct *vma,
>> unsigned long address,
>> ret = do_adjust_pte(vma, address, pfn, pte);
>> - if (ptl != vmf->ptl)
>> + if (need_lock)
>> spin_unlock(ptl);
>> pte_unmap(pte);
>> @@ -123,16 +122,17 @@ static int adjust_pte(struct vm_area_struct
>> *vma, unsigned long address,
>> static void
>> make_coherent(struct address_space *mapping, struct vm_area_struct
>> *vma,
>> - unsigned long addr, pte_t *ptep, unsigned long pfn,
>> - struct vm_fault *vmf)
>> + unsigned long addr, pte_t *ptep, unsigned long pfn)
>> {
>> struct mm_struct *mm = vma->vm_mm;
>> struct vm_area_struct *mpnt;
>> unsigned long offset;
>> + unsigned long start;
>> pgoff_t pgoff;
>> int aliases = 0;
>> pgoff = vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT);
>> + start = ALIGN_DOWN(addr, PMD_SIZE);
>
> I assume you can come up with a better name than "start" :)
>
> aligned_addr ... pmd_start_addr ...
>
> Maybe simply
>
> pmd_start_addr = ALIGN_DOWN(addr, PMD_SIZE);
> pmd_end_addr = addr + PMD_SIZE;
you mean:
pmd_end_addr = pmd_start_addr + PMD_SIZE;
Right?
>
> Then the comparison below also becomes easier to read.
>
>> /*
>> * If we have any shared mappings that are in the same mm
>> @@ -141,6 +141,14 @@ make_coherent(struct address_space *mapping,
>> struct vm_area_struct *vma,
>> */
>> flush_dcache_mmap_lock(mapping);
>> vma_interval_tree_foreach(mpnt, &mapping->i_mmap, pgoff, pgoff) {
>> + unsigned long mpnt_addr;
>> + /*
>> + * If we are using split PTE locks, then we need to take the pte
>> + * lock. Otherwise we are using shared mm->page_table_lock which
>> + * is already locked, thus cannot take it.
>> + */
>> + bool need_lock = IS_ENABLED(CONFIG_SPLIT_PTE_PTLOCKS);
>
> Nit: move "unsigned long mpnt_addr;" below this longer variable+init.
OK, will do.
>
>> +
>> /*
>> * If this VMA is not in our MM, we can ignore it.
>> * Note that we intentionally mask out the VMA
>> @@ -151,7 +159,15 @@ make_coherent(struct address_space *mapping,
>> struct vm_area_struct *vma,
>> if (!(mpnt->vm_flags & VM_MAYSHARE))
>> continue;
>> offset = (pgoff - mpnt->vm_pgoff) << PAGE_SHIFT;
>> - aliases += adjust_pte(mpnt, mpnt->vm_start + offset, pfn, vmf);
>> + mpnt_addr = mpnt->vm_start + offset;
>> + /*
>> + * If mpnt_addr and addr are mapped to the same PTE page, there
>> + * is no need to hold the pte lock again, otherwise a deadlock
>> + * will occur.
>
> /*
> * Avoid deadlocks by not grabbing the PTE lock if we already hold the
> * PTE lock of this PTE table in the caller.
> */
Maybe just:
/* Avoid deadlocks by not grabbing the same PTE lock again. */
Thanks,
Qi
>
> ?
>
>> + */
>> + if (mpnt_addr >= start && mpnt_addr - start < PMD_SIZE)
>> + need_lock = false;
>
>
>
On 12.02.25 09:28, Qi Zheng wrote:
>
>
> On 2025/2/12 16:20, David Hildenbrand wrote:
>> On 12.02.25 07:40, Qi Zheng wrote:
>>> When update_mmu_cache_range() is called by update_mmu_cache(), the vmf
>>> parameter is NULL, which will cause a NULL pointer dereference issue in
>>> adjust_pte():
>>>
>>> Unable to handle kernel NULL pointer dereference at virtual address
>>> 00000030 when read
>>> Hardware name: Atmel AT91SAM9
>>> PC is at update_mmu_cache_range+0x1e0/0x278
>>> LR is at pte_offset_map_rw_nolock+0x18/0x2c
>>> Call trace:
>>> update_mmu_cache_range from remove_migration_pte+0x29c/0x2ec
>>> remove_migration_pte from rmap_walk_file+0xcc/0x130
>>> rmap_walk_file from remove_migration_ptes+0x90/0xa4
>>> remove_migration_ptes from migrate_pages_batch+0x6d4/0x858
>>> migrate_pages_batch from migrate_pages+0x188/0x488
>>> migrate_pages from compact_zone+0x56c/0x954
>>> compact_zone from compact_node+0x90/0xf0
>>> compact_node from kcompactd+0x1d4/0x204
>>> kcompactd from kthread+0x120/0x12c
>>> kthread from ret_from_fork+0x14/0x38
>>> Exception stack(0xc0d8bfb0 to 0xc0d8bff8)
>>>
>>> To fix it, do not rely on whether 'ptl' is equal to decide whether to
>>> hold
>>> the pte lock, but decide it by whether CONFIG_SPLIT_PTE_PTLOCKS is
>>> enabled. In addition, if two vmas map to the same PTE page, there is no
>>> need to hold the pte lock again, otherwise a deadlock will occur. Just
>>> add
>>> the need_lock parameter to let adjust_pte() know this information.
>>>
>>> Reported-by: Ezra Buehler <ezra@easyb.ch>
>>> Closes:
>>> https://lore.kernel.org/lkml/CAM1KZSmZ2T_riHvay+7cKEFxoPgeVpHkVFTzVVEQ1BO0cLkHEQ@mail.gmail.com/
>>> Fixes: fc9c45b71f43 ("arm: adjust_pte() use pte_offset_map_rw_nolock()")
>>> Cc: stable@vger.kernel.org
>>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
>>> ---
>>> arch/arm/mm/fault-armv.c | 40 ++++++++++++++++++++++++++++------------
>>> 1 file changed, 28 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
>>> index 2bec87c3327d2..3627bf0957c75 100644
>>> --- a/arch/arm/mm/fault-armv.c
>>> +++ b/arch/arm/mm/fault-armv.c
>>> @@ -62,7 +62,7 @@ static int do_adjust_pte(struct vm_area_struct *vma,
>>> unsigned long address,
>>> }
>>> static int adjust_pte(struct vm_area_struct *vma, unsigned long
>>> address,
>>> - unsigned long pfn, struct vm_fault *vmf)
>>> + unsigned long pfn, bool need_lock)
>>> {
>>> spinlock_t *ptl;
>>> pgd_t *pgd;
>>> @@ -99,12 +99,11 @@ static int adjust_pte(struct vm_area_struct *vma,
>>> unsigned long address,
>>> if (!pte)
>>> return 0;
>>> - /*
>>> - * If we are using split PTE locks, then we need to take the page
>>> - * lock here. Otherwise we are using shared mm->page_table_lock
>>> - * which is already locked, thus cannot take it.
>>> - */
>>> - if (ptl != vmf->ptl) {
>>> + if (need_lock) {
>>> + /*
>>> + * Use nested version here to indicate that we are already
>>> + * holding one similar spinlock.
>>> + */
>>> spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
>>> if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pmd)))) {
>>> pte_unmap_unlock(pte, ptl);
>>> @@ -114,7 +113,7 @@ static int adjust_pte(struct vm_area_struct *vma,
>>> unsigned long address,
>>> ret = do_adjust_pte(vma, address, pfn, pte);
>>> - if (ptl != vmf->ptl)
>>> + if (need_lock)
>>> spin_unlock(ptl);
>>> pte_unmap(pte);
>>> @@ -123,16 +122,17 @@ static int adjust_pte(struct vm_area_struct
>>> *vma, unsigned long address,
>>> static void
>>> make_coherent(struct address_space *mapping, struct vm_area_struct
>>> *vma,
>>> - unsigned long addr, pte_t *ptep, unsigned long pfn,
>>> - struct vm_fault *vmf)
>>> + unsigned long addr, pte_t *ptep, unsigned long pfn)
>>> {
>>> struct mm_struct *mm = vma->vm_mm;
>>> struct vm_area_struct *mpnt;
>>> unsigned long offset;
>>> + unsigned long start;
>>> pgoff_t pgoff;
>>> int aliases = 0;
>>> pgoff = vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT);
>>> + start = ALIGN_DOWN(addr, PMD_SIZE);
>>
>> I assume you can come up with a better name than "start" :)
>>
>> aligned_addr ... pmd_start_addr ...
>>
>> Maybe simply
>>
>> pmd_start_addr = ALIGN_DOWN(addr, PMD_SIZE);
>> pmd_end_addr = addr + PMD_SIZE;
>
> you mean:
>
> pmd_end_addr = pmd_start_addr + PMD_SIZE;
>
> Right?
Yes :)
>>
>>> +
>>> /*
>>> * If this VMA is not in our MM, we can ignore it.
>>> * Note that we intentionally mask out the VMA
>>> @@ -151,7 +159,15 @@ make_coherent(struct address_space *mapping,
>>> struct vm_area_struct *vma,
>>> if (!(mpnt->vm_flags & VM_MAYSHARE))
>>> continue;
>>> offset = (pgoff - mpnt->vm_pgoff) << PAGE_SHIFT;
>>> - aliases += adjust_pte(mpnt, mpnt->vm_start + offset, pfn, vmf);
>>> + mpnt_addr = mpnt->vm_start + offset;
>>> + /*
>>> + * If mpnt_addr and addr are mapped to the same PTE page, there
>>> + * is no need to hold the pte lock again, otherwise a deadlock
>>> + * will occur.
>>
>> /*
>> * Avoid deadlocks by not grabbing the PTE lock if we already hold the
>> * PTE lock of this PTE table in the caller.
>> */
>
> Maybe just:
>
> /* Avoid deadlocks by not grabbing the same PTE lock again. */
>
Agreed.
--
Cheers,
David / dhildenb
Hi Qi, Thanks for the fix. I will test it as well as I can. On Wed, Feb 12, 2025 at 7:41 AM Qi Zheng <zhengqi.arch@bytedance.com> wrote: > > When update_mmu_cache_range() is called by update_mmu_cache(), the vmf > parameter is NULL, which will cause a NULL pointer dereference issue in > adjust_pte(): > > Unable to handle kernel NULL pointer dereference at virtual address 00000030 when read > Hardware name: Atmel AT91SAM9 > PC is at update_mmu_cache_range+0x1e0/0x278 > LR is at pte_offset_map_rw_nolock+0x18/0x2c > Call trace: > update_mmu_cache_range from remove_migration_pte+0x29c/0x2ec > remove_migration_pte from rmap_walk_file+0xcc/0x130 > rmap_walk_file from remove_migration_ptes+0x90/0xa4 > remove_migration_ptes from migrate_pages_batch+0x6d4/0x858 > migrate_pages_batch from migrate_pages+0x188/0x488 > migrate_pages from compact_zone+0x56c/0x954 > compact_zone from compact_node+0x90/0xf0 > compact_node from kcompactd+0x1d4/0x204 > kcompactd from kthread+0x120/0x12c > kthread from ret_from_fork+0x14/0x38 > Exception stack(0xc0d8bfb0 to 0xc0d8bff8) > > To fix it, do not rely on whether 'ptl' is equal to decide whether to hold > the pte lock, but decide it by whether CONFIG_SPLIT_PTE_PTLOCKS is > enabled. In addition, if two vmas map to the same PTE page, there is no > need to hold the pte lock again, otherwise a deadlock will occur. Just add > the need_lock parameter to let adjust_pte() know this information. > > Reported-by: Ezra Buehler <ezra@easyb.ch> Perhaps a detail but, maybe better use "Ezra Buehler <ezra.buehler@husqvarnagroup.com>" here. Cheers, Ezra.
Hi Ezra, On 2025/2/12 15:27, Ezra Buehler wrote: > Hi Qi, > > Thanks for the fix. I will test it as well as I can. Thanks! > > On Wed, Feb 12, 2025 at 7:41 AM Qi Zheng <zhengqi.arch@bytedance.com> wrote: >> >> When update_mmu_cache_range() is called by update_mmu_cache(), the vmf >> parameter is NULL, which will cause a NULL pointer dereference issue in >> adjust_pte(): >> >> Unable to handle kernel NULL pointer dereference at virtual address 00000030 when read >> Hardware name: Atmel AT91SAM9 >> PC is at update_mmu_cache_range+0x1e0/0x278 >> LR is at pte_offset_map_rw_nolock+0x18/0x2c >> Call trace: >> update_mmu_cache_range from remove_migration_pte+0x29c/0x2ec >> remove_migration_pte from rmap_walk_file+0xcc/0x130 >> rmap_walk_file from remove_migration_ptes+0x90/0xa4 >> remove_migration_ptes from migrate_pages_batch+0x6d4/0x858 >> migrate_pages_batch from migrate_pages+0x188/0x488 >> migrate_pages from compact_zone+0x56c/0x954 >> compact_zone from compact_node+0x90/0xf0 >> compact_node from kcompactd+0x1d4/0x204 >> kcompactd from kthread+0x120/0x12c >> kthread from ret_from_fork+0x14/0x38 >> Exception stack(0xc0d8bfb0 to 0xc0d8bff8) >> >> To fix it, do not rely on whether 'ptl' is equal to decide whether to hold >> the pte lock, but decide it by whether CONFIG_SPLIT_PTE_PTLOCKS is >> enabled. In addition, if two vmas map to the same PTE page, there is no >> need to hold the pte lock again, otherwise a deadlock will occur. Just add >> the need_lock parameter to let adjust_pte() know this information. >> >> Reported-by: Ezra Buehler <ezra@easyb.ch> > > Perhaps a detail but, maybe better use "Ezra Buehler > <ezra.buehler@husqvarnagroup.com>" here. Got it. Will wait for your test results first. Thanks, Qi > > Cheers, > Ezra.
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