tree 53df4d3dd0fbd81b79d5cdb63cf0d11853307a6b
parent 0cfc11ed45e4c00750039e5a18c0fc0d681e19db
author Andrew Morton <[EMAIL PROTECTED]> Thu, 28 Jul 2005 01:43:54 -0700
committer Linus Torvalds <[EMAIL PROTECTED]> Thu, 28 Jul 2005 06:25:53 -0700
[PATCH] check_user_page_readable() deadlock fix
Fix bug identifued by Richard Purdie <[EMAIL PROTECTED]>.
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: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
mm/memory.c | 25 +++++++++++++++----------
1 files changed, 15 insertions(+), 10 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -776,8 +776,8 @@ unsigned long zap_page_range(struct vm_a
* 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, unsi
pfn = pte_pfn(pte);
if (pfn_valid(pfn)) {
page = pfn_to_page(pfn);
- if (write && !pte_dirty(pte) && !PageDirty(page))
- set_page_dirty(page);
- mark_page_accessed(page);
+ if (accessed) {
+ if (write && !pte_dirty(pte) &&!PageDirty(page))
+ set_page_dirty(page);
+ mark_page_accessed(page);
+ }
return page;
}
}
@@ -829,16 +831,19 @@ out:
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);
-
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