Commit 1aaf18ff authored by Andrew Morton's avatar Andrew Morton Committed by Linus Torvalds
Browse files

[PATCH] check_user_page_readable() deadlock fix 



Fix bug identifued by Richard Purdie <rpurdie@rpsys.net>.

oprofile calls check_user_page_readable() from interrupt context, so we
deadlock over various VFS locks.

But check_user_page_readable() doesn't imply either a read or a write of the
page's contents.  Change __follow_page() so that check_user_page_readable()
can tell __follow_page() that we're not accessing the page's contents, and use
that info to avoid the troublesome lock-takings.

Also, make follow_page() inline for the single callsite in memory.c to save a
bit of stack space.

Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 0cfc11ed

mm/memory.c

+15 −10
Original line number Diff line number Diff line
@@ -776,8 +776,8 @@ unsigned long zap_page_range(struct vm_area_struct *vma, unsigned long address, 
 * Do a quick page-table lookup for a single page.

 * mm->page_table_lock must be held.

 */

static struct page *

__follow_page(struct mm_struct *mm, unsigned long address, int read, int write)

static struct page *__follow_page(struct mm_struct *mm, unsigned long address,

			int read, int write, int accessed)

{

	pgd_t *pgd;

	pud_t *pud;
@@ -818,9 +818,11 @@ __follow_page(struct mm_struct *mm, unsigned long address, int read, int write) 
		pfn = pte_pfn(pte);

		if (pfn_valid(pfn)) {

			page = pfn_to_page(pfn);

			if (accessed) {

				if (write && !pte_dirty(pte) &&!PageDirty(page))

					set_page_dirty(page);

				mark_page_accessed(page);

			}

			return page;

		}

	}
@@ -829,16 +831,19 @@ __follow_page(struct mm_struct *mm, unsigned long address, int read, int write) 
	return NULL;

}



struct page *

inline struct page *

follow_page(struct mm_struct *mm, unsigned long address, int write)

{

	return __follow_page(mm, address, /*read*/0, write);

	return __follow_page(mm, address, 0, write, 1);

}



int

check_user_page_readable(struct mm_struct *mm, unsigned long address)

/*

 * check_user_page_readable() can be called frm niterrupt context by oprofile,

 * so we need to avoid taking any non-irq-safe locks

 */

int check_user_page_readable(struct mm_struct *mm, unsigned long address)

{

	return __follow_page(mm, address, /*read*/1, /*write*/0) != NULL;

	return __follow_page(mm, address, 1, 0, 0) != NULL;

}

EXPORT_SYMBOL(check_user_page_readable);