Hello,
Without this patch we can deadlock in the page_table_lock with NR_CPUS
< 4 or THP on, with this patch we hopefully won't deadlock in the
pgd_lock (if taken from irq). I can't see anything taking it from irq
(maybe aio? to check I also tried the libaio testuite with no apparent
VM_BUG_ON triggering), so unless somebody sees it, I think we should
apply it. I've been running for a while with this patch applied
without apparent problems. Other archs may follow suit if it's proven
that there's nothing taking the pgd_lock from irq.
===
Subject: fix pgd_lock deadlock
From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
It's forbidden to take the page_table_lock with the irq disabled or if there's
contention the IPIs (for tlb flushes) sent with the page_table_lock held will
never run leading to a deadlock.
Apparently nobody takes the pgd_lock from irq so the _irqsave can be removed.
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
arch/x86/mm/fault.c | 8 ++++----
arch/x86/mm/init_64.c | 7 ++++---
arch/x86/mm/pageattr.c | 21 +++++++++++----------
arch/x86/mm/pgtable.c | 13 ++++++-------
arch/x86/xen/mmu.c | 10 ++++------
5 files changed, 29 insertions(+), 30 deletions(-)
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -229,15 +229,15 @@ void vmalloc_sync_all(void)
for (address = VMALLOC_START & PMD_MASK;
address >= TASK_SIZE && address < FIXADDR_TOP;
address += PMD_SIZE) {
-
- unsigned long flags;
struct page *page;
- spin_lock_irqsave(&pgd_lock, flags);
+ VM_BUG_ON(in_interrupt());
+ spin_lock(&pgd_lock);
list_for_each_entry(page, &pgd_list, lru) {
spinlock_t *pgt_lock;
pmd_t *ret;
+ /* the pgt_lock only for Xen */
pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
spin_lock(pgt_lock);
@@ -247,7 +247,7 @@ void vmalloc_sync_all(void)
if (!ret)
break;
}
- spin_unlock_irqrestore(&pgd_lock, flags);
+ spin_unlock(&pgd_lock);
}
}
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -105,18 +105,19 @@ void sync_global_pgds(unsigned long star
for (address = start; address <= end; address += PGDIR_SIZE) {
const pgd_t *pgd_ref = pgd_offset_k(address);
- unsigned long flags;
struct page *page;
if (pgd_none(*pgd_ref))
continue;
- spin_lock_irqsave(&pgd_lock, flags);
+ VM_BUG_ON(in_interrupt());
+ spin_lock(&pgd_lock);
list_for_each_entry(page, &pgd_list, lru) {
pgd_t *pgd;
spinlock_t *pgt_lock;
pgd = (pgd_t *)page_address(page) + pgd_index(address);
+ /* the pgt_lock only for Xen */
pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
spin_lock(pgt_lock);
@@ -128,7 +129,7 @@ void sync_global_pgds(unsigned long star
spin_unlock(pgt_lock);
}
- spin_unlock_irqrestore(&pgd_lock, flags);
+ spin_unlock(&pgd_lock);
}
}
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -57,12 +57,11 @@ static unsigned long direct_pages_count[
void update_page_count(int level, unsigned long pages)
{
- unsigned long flags;
-
/* Protect against CPA */
- spin_lock_irqsave(&pgd_lock, flags);
+ VM_BUG_ON(in_interrupt());
+ spin_lock(&pgd_lock);
direct_pages_count[level] += pages;
- spin_unlock_irqrestore(&pgd_lock, flags);
+ spin_unlock(&pgd_lock);
}
static void split_page_count(int level)
@@ -394,7 +393,7 @@ static int
try_preserve_large_page(pte_t *kpte, unsigned long address,
struct cpa_data *cpa)
{
- unsigned long nextpage_addr, numpages, pmask, psize, flags, addr, pfn;
+ unsigned long nextpage_addr, numpages, pmask, psize, addr, pfn;
pte_t new_pte, old_pte, *tmp;
pgprot_t old_prot, new_prot, req_prot;
int i, do_split = 1;
@@ -403,7 +402,8 @@ try_preserve_large_page(pte_t *kpte, uns
if (cpa->force_split)
return 1;
- spin_lock_irqsave(&pgd_lock, flags);
+ VM_BUG_ON(in_interrupt());
+ spin_lock(&pgd_lock);
/*
* Check for races, another CPU might have split this page
* up already:
@@ -498,14 +498,14 @@ try_preserve_large_page(pte_t *kpte, uns
}
out_unlock:
- spin_unlock_irqrestore(&pgd_lock, flags);
+ spin_unlock(&pgd_lock);
return do_split;
}
static int split_large_page(pte_t *kpte, unsigned long address)
{
- unsigned long flags, pfn, pfninc = 1;
+ unsigned long pfn, pfninc = 1;
unsigned int i, level;
pte_t *pbase, *tmp;
pgprot_t ref_prot;
@@ -519,7 +519,8 @@ static int split_large_page(pte_t *kpte,
if (!base)
return -ENOMEM;
- spin_lock_irqsave(&pgd_lock, flags);
+ VM_BUG_ON(in_interrupt());
+ spin_lock(&pgd_lock);
/*
* Check for races, another CPU might have split this page
* up for us already:
@@ -591,7 +592,7 @@ out_unlock:
*/
if (base)
__free_page(base);
- spin_unlock_irqrestore(&pgd_lock, flags);
+ spin_unlock(&pgd_lock);
return 0;
}
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -121,14 +121,13 @@ static void pgd_ctor(struct mm_struct *m
static void pgd_dtor(pgd_t *pgd)
{
- unsigned long flags; /* can be called from interrupt context */
-
if (SHARED_KERNEL_PMD)
return;
- spin_lock_irqsave(&pgd_lock, flags);
+ VM_BUG_ON(in_interrupt());
+ spin_lock(&pgd_lock);
pgd_list_del(pgd);
- spin_unlock_irqrestore(&pgd_lock, flags);
+ spin_unlock(&pgd_lock);
}
/*
@@ -260,7 +259,6 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
{
pgd_t *pgd;
pmd_t *pmds[PREALLOCATED_PMDS];
- unsigned long flags;
pgd = (pgd_t *)__get_free_page(PGALLOC_GFP);
@@ -280,12 +278,13 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
* respect to anything walking the pgd_list, so that they
* never see a partially populated pgd.
*/
- spin_lock_irqsave(&pgd_lock, flags);
+ VM_BUG_ON(in_interrupt());
+ spin_lock(&pgd_lock);
pgd_ctor(mm, pgd);
pgd_prepopulate_pmd(mm, pgd, pmds);
- spin_unlock_irqrestore(&pgd_lock, flags);
+ spin_unlock(&pgd_lock);
return pgd;
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -986,10 +986,9 @@ static void xen_pgd_pin(struct mm_struct
*/
void xen_mm_pin_all(void)
{
- unsigned long flags;
struct page *page;
- spin_lock_irqsave(&pgd_lock, flags);
+ spin_lock(&pgd_lock);
list_for_each_entry(page, &pgd_list, lru) {
if (!PagePinned(page)) {
@@ -998,7 +997,7 @@ void xen_mm_pin_all(void)
}
}
- spin_unlock_irqrestore(&pgd_lock, flags);
+ spin_unlock(&pgd_lock);
}
/*
@@ -1099,10 +1098,9 @@ static void xen_pgd_unpin(struct mm_stru
*/
void xen_mm_unpin_all(void)
{
- unsigned long flags;
struct page *page;
- spin_lock_irqsave(&pgd_lock, flags);
+ spin_lock(&pgd_lock);
list_for_each_entry(page, &pgd_list, lru) {
if (PageSavePinned(page)) {
@@ -1112,7 +1110,7 @@ void xen_mm_unpin_all(void)
}
}
- spin_unlock_irqrestore(&pgd_lock, flags);
+ spin_unlock(&pgd_lock);
}
void xen_activate_mm(struct mm_struct *prev, struct mm_struct *next)
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