[2/3] hugetlbfs: close race between MADV_DONTNEED and page fault
Commit Message
From: Rik van Riel <riel@surriel.com>
Malloc libraries, like jemalloc and tcalloc, take decisions on when
to call madvise independently from the code in the main application.
This sometimes results in the application page faulting on an address,
right after the malloc library has shot down the backing memory with
MADV_DONTNEED.
Usually this is harmless, because we always have some 4kB pages
sitting around to satisfy a page fault. However, with hugetlbfs
systems often allocate only the exact number of huge pages that
the application wants.
Due to TLB batching, hugetlbfs MADV_DONTNEED will free pages outside of
any lock taken on the page fault path, which can open up the following
race condition:
CPU 1 CPU 2
MADV_DONTNEED
unmap page
shoot down TLB entry
page fault
fail to allocate a huge page
killed with SIGBUS
free page
Fix that race by pulling the locking from __unmap_hugepage_final_range
into helper functions called from zap_page_range_single. This ensures
page faults stay locked out of the MADV_DONTNEED VMA until the
huge pages have actually been freed.
Signed-off-by: Rik van Riel <riel@surriel.com>
---
include/linux/hugetlb.h | 35 +++++++++++++++++++++++++++++++++--
mm/hugetlb.c | 20 +++++++++++---------
mm/memory.c | 13 ++++++++-----
3 files changed, 52 insertions(+), 16 deletions(-)
Comments
On 09/30/23 20:55, riel@surriel.com wrote:
> From: Rik van Riel <riel@surriel.com>
>
> Malloc libraries, like jemalloc and tcalloc, take decisions on when
> to call madvise independently from the code in the main application.
>
> This sometimes results in the application page faulting on an address,
> right after the malloc library has shot down the backing memory with
> MADV_DONTNEED.
>
> Usually this is harmless, because we always have some 4kB pages
> sitting around to satisfy a page fault. However, with hugetlbfs
> systems often allocate only the exact number of huge pages that
> the application wants.
>
> Due to TLB batching, hugetlbfs MADV_DONTNEED will free pages outside of
> any lock taken on the page fault path, which can open up the following
> race condition:
>
> CPU 1 CPU 2
>
> MADV_DONTNEED
> unmap page
> shoot down TLB entry
> page fault
> fail to allocate a huge page
> killed with SIGBUS
> free page
>
> Fix that race by pulling the locking from __unmap_hugepage_final_range
> into helper functions called from zap_page_range_single. This ensures
> page faults stay locked out of the MADV_DONTNEED VMA until the
> huge pages have actually been freed.
>
> Signed-off-by: Rik van Riel <riel@surriel.com>
> ---
> include/linux/hugetlb.h | 35 +++++++++++++++++++++++++++++++++--
> mm/hugetlb.c | 20 +++++++++++---------
> mm/memory.c | 13 ++++++++-----
Hi Rik,
Something is not right here. I have not looked closely at the patch,
but running libhugetlbfs test suite hits this NULL deref in misalign (2M: 32).
[ 51.891236] BUG: kernel NULL pointer dereference, address: 00000000000001c0
[ 51.892420] #PF: supervisor read access in kernel mode
[ 51.893353] #PF: error_code(0x0000) - not-present page
[ 51.894207] PGD 80000001eeac0067 P4D 80000001eeac0067 PUD 1fa577067 PMD 0
[ 51.895299] Oops: 0000 [#1] PREEMPT SMP PTI
[ 51.896010] CPU: 0 PID: 1004 Comm: misalign Not tainted 6.6.0-rc3-next-20230925+ #13
[ 51.897285] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc37 04/01/2014
[ 51.898674] RIP: 0010:__hugetlb_zap_begin+0x76/0x90
[ 51.899488] Code: 06 48 8b 3a 48 39 cf 73 11 48 81 c7 ff ff ff 3f 48 81 e7 00 00 00 c0 48 89 3a 48 89 df e8 42 cd ff ff 48 8b 83 88 00 00 00 5b <48> 8b b8 c0 01 00 00 48 81 c7 28 01 00 00 e9 87 3b 91 00 0f 1f 80
[ 51.902194] RSP: 0018:ffffc9000487bbf0 EFLAGS: 00010246
[ 51.903019] RAX: 0000000000000000 RBX: 00000000f7a00000 RCX: 00000000c0000000
[ 51.904088] RDX: 0000000000440073 RSI: ffffc9000487bc00 RDI: ffff8881fa71dcb8
[ 51.905207] RBP: 00000000f7800000 R08: 00000000f7a00000 R09: 00000000f7a00000
[ 51.906284] R10: ffff8881fb5b8040 R11: ffff8881fb5b89b0 R12: ffff8881fa71dcb8
[ 51.907351] R13: ffffc9000487bd80 R14: ffffc9000487bc78 R15: 0000000000000001
[ 51.908648] FS: 0000000000000000(0000) GS:ffff888277c00000(0063) knlGS:00000000f7c99700
[ 51.910613] CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033
[ 51.911983] CR2: 00000000000001c0 CR3: 00000001fa412005 CR4: 0000000000370ef0
[ 51.913417] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 51.914535] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 51.915602] Call Trace:
[ 51.916069] <TASK>
[ 51.916480] ? __die+0x1f/0x70
[ 51.917057] ? page_fault_oops+0x159/0x450
[ 51.917737] ? do_user_addr_fault+0x65/0x850
[ 51.919360] ? exc_page_fault+0x6d/0x1c0
[ 51.920021] ? asm_exc_page_fault+0x22/0x30
[ 51.920712] ? __hugetlb_zap_begin+0x76/0x90
[ 51.921440] unmap_vmas+0xb3/0x100
[ 51.922057] unmap_region.constprop.0+0xcc/0x140
[ 51.922837] ? lock_release+0x142/0x290
[ 51.923474] ? preempt_count_add+0x47/0xa0
[ 51.924150] mmap_region+0x565/0xab0
[ 51.924809] do_mmap+0x35a/0x520
[ 51.925384] vm_mmap_pgoff+0xdf/0x200
[ 51.926008] ksys_mmap_pgoff+0x18f/0x200
[ 51.926834] ? syscall_enter_from_user_mode_prepare+0x19/0x60
[ 51.928006] __do_fast_syscall_32+0x68/0x100
[ 51.928962] do_fast_syscall_32+0x2f/0x70
[ 51.929896] entry_SYSENTER_compat_after_hwframe+0x7b/0x8d
I think you previously built libhugetlbfs, so hopefully you can recreate.
The stack trace (and test) suggest hugetlbfs_file_mmap returns an error
due to misalignment, and then we unmap the vma just previously created.
Looks code is now calling hugetlb_zap_begin before unmap_single_vma.
The code/comment in unmap_single_vma mentions this special cleanup
case. Looks like vma->vm_file is NULL and __hugetlb_zap_begin is doing
a i_mmap_lock_write(vma->vm_file->f_mapping).
if (start != end) {
if (unlikely(is_vm_hugetlb_page(vma))) {
/*
* It is undesirable to test vma->vm_file as it
* should be non-null for valid hugetlb area.
* However, vm_file will be NULL in the error
* cleanup path of mmap_region. When
* hugetlbfs ->mmap method fails,
* mmap_region() nullifies vma->vm_file
* before calling this function to clean up.
* Since no pte has actually been setup, it is
* safe to do nothing in this case.
*/
if (vma->vm_file) {
zap_flags_t zap_flags = details ?
details->zap_flags : 0;
__unmap_hugepage_range_final(tlb, vma, start, end,
NULL, zap_flags);
}
Looks like vma->vm_file is NULL and __hugetlb_zap_begin is trying to do
i_mmap_lock_write(vma->vm_file->f_mapping).
Guess I did look closely. :)
On Sun, 2023-10-01 at 21:39 -0700, Mike Kravetz wrote:
>
> Looks like vma->vm_file is NULL and __hugetlb_zap_begin is trying to
> do
> i_mmap_lock_write(vma->vm_file->f_mapping).
>
> Guess I did look closely. :)
Ugh. It looks like the fix for this bug ended up getting pulled
into patch 3, instead of patch 2. I've had it in my code for a
while now :/
Let me move the fix for this thing into patch 2.
void __hugetlb_zap_begin(struct vm_area_struct *vma,
unsigned long *start, unsigned long *end)
{
adjust_range_if_pmd_sharing_possible(vma, start, end);
hugetlb_vma_lock_write(vma);
if (vma->vm_file)
i_mmap_lock_write(vma->vm_file->f_mapping);
}
On Sun, 2023-10-01 at 21:39 -0700, Mike Kravetz wrote:
>
> Something is not right here. I have not looked closely at the patch,
> but running libhugetlbfs test suite hits this NULL deref in misalign
> (2M: 32).
Hi Mike,
fixing the null dereference was easy, but I continued running
into a test case failure with linkhuge_rw. After tweaking the
code in my patches quite a few times, I finally ran out of
ideas and tried it on a tree without my patches.
I still see the test failure on upstream
2cf0f7156238 ("Merge tag 'nfs-for-6.6-2' of git://git.linux-
nfs.org/projects/anna/linux-nfs")
This is with a modern glibc, and the __morecore assignments
in libhugetlbfs/morecore.c commented out.
HUGETLB_ELFMAP=R HUGETLB_SHARE=1 linkhuge_rw (2M: 32): Pool state:
(('hugepages-2048kB', (('free_hugepages', 1), ('resv_hugepages', 0),
('surplus_hugepages', 0), ('nr_hugepages_mempolicy', 1),
('nr_hugepages', 1), ('nr_overcommit_hugepages', 0))),)
Hugepage pool state not preserved!
BEFORE: (('hugepages-2048kB', (('free_hugepages', 1),
('resv_hugepages', 0), ('surplus_hugepages', 0),
('nr_hugepages_mempolicy', 1), ('nr_hugepages', 1),
('nr_overcommit_hugepages', 0))),)
AFTER: (('hugepages-2048kB', (('free_hugepages', 0), ('resv_hugepages',
0), ('surplus_hugepages', 0), ('nr_hugepages_mempolicy', 1),
('nr_hugepages', 1), ('nr_overcommit_hugepages', 0))),)
It may take a little while to figure this one out. I did some
bpftracing, but don't have a real smoking gun yet. The trace
certainly shows the last user of the leaked huge page going
into __unmap_hugepage_range.
On 10/03/23 15:35, Rik van Riel wrote:
> On Sun, 2023-10-01 at 21:39 -0700, Mike Kravetz wrote:
> >
> > Something is not right here. I have not looked closely at the patch,
> > but running libhugetlbfs test suite hits this NULL deref in misalign
> > (2M: 32).
>
> Hi Mike,
>
> fixing the null dereference was easy, but I continued running
> into a test case failure with linkhuge_rw. After tweaking the
> code in my patches quite a few times, I finally ran out of
> ideas and tried it on a tree without my patches.
>
> I still see the test failure on upstream
> 2cf0f7156238 ("Merge tag 'nfs-for-6.6-2' of git://git.linux-
> nfs.org/projects/anna/linux-nfs")
>
> This is with a modern glibc, and the __morecore assignments
> in libhugetlbfs/morecore.c commented out.
>
>
> HUGETLB_ELFMAP=R HUGETLB_SHARE=1 linkhuge_rw (2M: 32): Pool state:
> (('hugepages-2048kB', (('free_hugepages', 1), ('resv_hugepages', 0),
> ('surplus_hugepages', 0), ('nr_hugepages_mempolicy', 1),
> ('nr_hugepages', 1), ('nr_overcommit_hugepages', 0))),)
> Hugepage pool state not preserved!
> BEFORE: (('hugepages-2048kB', (('free_hugepages', 1),
> ('resv_hugepages', 0), ('surplus_hugepages', 0),
> ('nr_hugepages_mempolicy', 1), ('nr_hugepages', 1),
> ('nr_overcommit_hugepages', 0))),)
> AFTER: (('hugepages-2048kB', (('free_hugepages', 0), ('resv_hugepages',
> 0), ('surplus_hugepages', 0), ('nr_hugepages_mempolicy', 1),
> ('nr_hugepages', 1), ('nr_overcommit_hugepages', 0))),)
>
Hi Rik,
When I started working on hugetlb several years ago, the following libhugetlbfs
tests failed. This was/is with a version of glibc that supports __morecore.
noresv-preserve-resv-page (2M: 32): FAIL mmap() 1: Invalid argument
HUGETLB_ELFMAP=RW linkhuge_rw (2M: 32): FAIL small_data is not hugepage
HUGETLB_ELFMAP=RW linkhuge_rw (2M: 64): FAIL small_data is not hugepage
HUGETLB_MINIMAL_COPY=no HUGETLB_ELFMAP=RW linkhuge_rw (2M: 32): FAIL small_data is not hugepage
HUGETLB_MINIMAL_COPY=no HUGETLB_ELFMAP=RW linkhuge_rw (2M: 64): FAIL small_data is not hugepage
HUGETLB_ELFMAP=RW HUGETLB_SHARE=0 linkhuge_rw (2M: 32): FAIL small_data is not hugepage
HUGETLB_ELFMAP=RW HUGETLB_SHARE=0 linkhuge_rw (2M: 64): FAIL small_data is not hugepage
HUGETLB_ELFMAP=RW HUGETLB_SHARE=1 linkhuge_rw (2M: 32): FAIL small_data is not hugepage
HUGETLB_ELFMAP=RW HUGETLB_SHARE=1 linkhuge_rw (2M: 64): FAIL small_data is not hugepage
alloc-instantiate-race shared (2M: 32): FAIL mmap() 1: Cannot allocate memory
alloc-instantiate-race private (2M: 32): FAIL mmap() 1: Cannot allocate memory
truncate_sigbus_versus_oom (2M: 32): FAIL mmap() reserving all pages: Invalid argument
mmap-gettest 10 2048 (2M: 32): FAIL Failed to mmap the hugetlb file: Invalid argument
shm-fork 10 2048 (2M: 32): FAIL shmget(): Invalid argument
shm-getraw 2048 /dev/full (2M: 32): FAIL shmget(): Invalid argument
I spent some time looking into the issues, but most were issues with the
tests themselves. I did not attempt to modify the tests, nor do I
remember all the issues.
Please consider the above failures normal and expected. That have been
this way for many years. Sorry for any waste of your time.
Of course, if you would like to look into these you are welcome.
On Tue, 2023-10-03 at 13:19 -0700, Mike Kravetz wrote:
> On 10/03/23 15:35, Rik van Riel wrote:
> > On Sun, 2023-10-01 at 21:39 -0700, Mike Kravetz wrote:
> > >
> > > Something is not right here. I have not looked closely at the
> > > patch,
> > > but running libhugetlbfs test suite hits this NULL deref in
> > > misalign
> > > (2M: 32).
> >
> > Hi Mike,
> >
> > fixing the null dereference was easy, but I continued running
> > into a test case failure with linkhuge_rw. After tweaking the
> > code in my patches quite a few times, I finally ran out of
> > ideas and tried it on a tree without my patches.
> >
> > I still see the test failure on upstream
> > 2cf0f7156238 ("Merge tag 'nfs-for-6.6-2' of git://git.linux-
> > nfs.org/projects/anna/linux-nfs")
> >
> > This is with a modern glibc, and the __morecore assignments
> > in libhugetlbfs/morecore.c commented out.
> >
> >
> > HUGETLB_ELFMAP=R HUGETLB_SHARE=1 linkhuge_rw (2M: 32): Pool state:
> > (('hugepages-2048kB', (('free_hugepages', 1), ('resv_hugepages',
> > 0),
> > ('surplus_hugepages', 0), ('nr_hugepages_mempolicy', 1),
> > ('nr_hugepages', 1), ('nr_overcommit_hugepages', 0))),)
> > Hugepage pool state not preserved!
> > BEFORE: (('hugepages-2048kB', (('free_hugepages', 1),
> > ('resv_hugepages', 0), ('surplus_hugepages', 0),
> > ('nr_hugepages_mempolicy', 1), ('nr_hugepages', 1),
> > ('nr_overcommit_hugepages', 0))),)
> > AFTER: (('hugepages-2048kB', (('free_hugepages', 0),
> > ('resv_hugepages',
> > 0), ('surplus_hugepages', 0), ('nr_hugepages_mempolicy', 1),
> > ('nr_hugepages', 1), ('nr_overcommit_hugepages', 0))),)
> >
>
> Please consider the above failures normal and expected. That have
> been
> this way for many years. Sorry for any waste of your time.
>
> Of course, if you would like to look into these you are welcome.
I'm not too worried about the test cases returning failure,
but having free_hugepages not go back to 1 after linkhuge_rw
exits looks bad.
In this case it appears that linkhuge_rw simply left behind
a file in /dev/hugepages when it died, and removing that file
returns free_hugepages back to what it should be.
I guess I'll go run the test cases without -c 1 :)
@@ -139,7 +139,7 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
void unmap_hugepage_range(struct vm_area_struct *,
unsigned long, unsigned long, struct page *,
zap_flags_t);
-void __unmap_hugepage_range_final(struct mmu_gather *tlb,
+void __unmap_hugepage_range(struct mmu_gather *tlb,
struct vm_area_struct *vma,
unsigned long start, unsigned long end,
struct page *ref_page, zap_flags_t zap_flags);
@@ -246,6 +246,25 @@ int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma,
void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,
unsigned long *start, unsigned long *end);
+extern void __hugetlb_zap_begin(struct vm_area_struct *vma,
+ unsigned long *begin, unsigned long *end);
+extern void __hugetlb_zap_end(struct vm_area_struct *vma,
+ struct zap_details *details);
+
+static inline void hugetlb_zap_begin(struct vm_area_struct *vma,
+ unsigned long *start, unsigned long *end)
+{
+ if (is_vm_hugetlb_page(vma))
+ __hugetlb_zap_begin(vma, start, end);
+}
+
+static inline void hugetlb_zap_end(struct vm_area_struct *vma,
+ struct zap_details *details)
+{
+ if (is_vm_hugetlb_page(vma))
+ __hugetlb_zap_end(vma, details);
+}
+
void hugetlb_vma_lock_read(struct vm_area_struct *vma);
void hugetlb_vma_unlock_read(struct vm_area_struct *vma);
void hugetlb_vma_lock_write(struct vm_area_struct *vma);
@@ -297,6 +316,18 @@ static inline void adjust_range_if_pmd_sharing_possible(
{
}
+static inline void hugetlb_zap_begin(
+ struct vm_area_struct *vma,
+ unsigned long *start, unsigned long *end)
+{
+}
+
+static inline void hugetlb_zap_end(
+ struct vm_area_struct *vma,
+ struct zap_details *details)
+{
+}
+
static inline struct page *hugetlb_follow_page_mask(
struct vm_area_struct *vma, unsigned long address, unsigned int flags,
unsigned int *page_mask)
@@ -442,7 +473,7 @@ static inline long hugetlb_change_protection(
return 0;
}
-static inline void __unmap_hugepage_range_final(struct mmu_gather *tlb,
+static inline void __unmap_hugepage_range(struct mmu_gather *tlb,
struct vm_area_struct *vma, unsigned long start,
unsigned long end, struct page *ref_page,
zap_flags_t zap_flags)
@@ -5306,9 +5306,9 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma,
return len + old_addr - old_end;
}
-static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
- unsigned long start, unsigned long end,
- struct page *ref_page, zap_flags_t zap_flags)
+void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
+ unsigned long start, unsigned long end,
+ struct page *ref_page, zap_flags_t zap_flags)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long address;
@@ -5435,16 +5435,18 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
tlb_flush_mmu_tlbonly(tlb);
}
-void __unmap_hugepage_range_final(struct mmu_gather *tlb,
- struct vm_area_struct *vma, unsigned long start,
- unsigned long end, struct page *ref_page,
- zap_flags_t zap_flags)
+void __hugetlb_zap_begin(struct vm_area_struct *vma,
+ unsigned long *start, unsigned long *end)
{
+ adjust_range_if_pmd_sharing_possible(vma, start, end);
hugetlb_vma_lock_write(vma);
i_mmap_lock_write(vma->vm_file->f_mapping);
+}
- /* mmu notification performed in caller */
- __unmap_hugepage_range(tlb, vma, start, end, ref_page, zap_flags);
+void __hugetlb_zap_end(struct vm_area_struct *vma,
+ struct zap_details *details)
+{
+ zap_flags_t zap_flags = details ? details->zap_flags : 0;
if (zap_flags & ZAP_FLAG_UNMAP) { /* final unmap */
/*
@@ -1683,7 +1683,7 @@ static void unmap_single_vma(struct mmu_gather *tlb,
if (vma->vm_file) {
zap_flags_t zap_flags = details ?
details->zap_flags : 0;
- __unmap_hugepage_range_final(tlb, vma, start, end,
+ __unmap_hugepage_range(tlb, vma, start, end,
NULL, zap_flags);
}
} else
@@ -1728,8 +1728,12 @@ void unmap_vmas(struct mmu_gather *tlb, struct ma_state *mas,
start_addr, end_addr);
mmu_notifier_invalidate_range_start(&range);
do {
- unmap_single_vma(tlb, vma, start_addr, end_addr, &details,
+ unsigned long start = start_addr;
+ unsigned long end = end_addr;
+ hugetlb_zap_begin(vma, &start, &end);
+ unmap_single_vma(tlb, vma, start, end, &details,
mm_wr_locked);
+ hugetlb_zap_end(vma, &details);
} while ((vma = mas_find(mas, tree_end - 1)) != NULL);
mmu_notifier_invalidate_range_end(&range);
}
@@ -1753,9 +1757,7 @@ void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
lru_add_drain();
mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
address, end);
- if (is_vm_hugetlb_page(vma))
- adjust_range_if_pmd_sharing_possible(vma, &range.start,
- &range.end);
+ hugetlb_zap_begin(vma, &range.start, &range.end);
tlb_gather_mmu(&tlb, vma->vm_mm);
update_hiwater_rss(vma->vm_mm);
mmu_notifier_invalidate_range_start(&range);
@@ -1766,6 +1768,7 @@ void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
unmap_single_vma(&tlb, vma, address, end, details, false);
mmu_notifier_invalidate_range_end(&range);
tlb_finish_mmu(&tlb);
+ hugetlb_zap_end(vma, details);
}
/**