Re: [PATCH] fix pgd_lock deadlock

Andrea Arcangeli
2011-02-16T14:50:27Z

On Wed, Feb 16, 2011 at 11:28:01AM +0100, Ingo Molnar wrote:
> The point both Thomas and Peter tried to point out to you, that adding 7 instances
> of redundant debug checks:
>
> + VM_BUG_ON(in_interrupt());
> + VM_BUG_ON(in_interrupt());
> + VM_BUG_ON(in_interrupt());
> + VM_BUG_ON(in_interrupt());
> + VM_BUG_ON(in_interrupt());
> + VM_BUG_ON(in_interrupt());
> + VM_BUG_ON(in_interrupt());
>
> to arch/x86/ is not acceptable, for the reasons stated. Please remove it from the
> patch.

Ok sorry, but whenever I'm asked if I tested my patch with lockdep, I
think if it was tested for other bugs, not to remove debug code
overlapping with some lockdep feature.

===
Subject: fix pgd_lock deadlock

From: Andrea Arcangeli <aarcange@redhat.com>

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@redhat.com>
---
arch/x86/mm/fault.c | 7 +++----
arch/x86/mm/init_64.c | 6 +++---
arch/x86/mm/pageattr.c | 18 ++++++++----------
arch/x86/mm/pgtable.c | 11 ++++-------
arch/x86/xen/mmu.c | 10 ++++------
5 files changed, 22 insertions(+), 30 deletions(-)

--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -229,15 +229,14 @@ 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);
+ 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 +246,7 @@ 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 +105,18 @@ 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);
+ 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 +128,7 @@ 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 +57,10 @@ 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);
+ 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 +392,7 @@ 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 +401,7 @@ try_preserve_large_page(pte_t *kpte, uns
if (cpa->force_split)
return 1;

- spin_lock_irqsave(&pgd_lock, flags);
+ spin_lock(&pgd_lock);
/*
* Check for races, another CPU might have split this page
* up already:
@@ -498,14 +496,14 @@ 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 +517,7 @@ static int split_large_page(pte_t *kpte,
if (!base)
return -ENOMEM;

- spin_lock_irqsave(&pgd_lock, flags);
+ spin_lock(&pgd_lock);
/*
* Check for races, another CPU might have split this page
* up for us already:
@@ -591,7 +589,7 @@ 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 +121,12 @@ 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);
+ spin_lock(&pgd_lock);
pgd_list_del(pgd);
- spin_unlock_irqrestore(&pgd_lock, flags);
+ spin_unlock(&pgd_lock);
}

/*
@@ -260,7 +258,6 @@ 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 +277,12 @@ 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);
+ 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)