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authorLinus Torvalds <torvalds@linux-foundation.org>2012-05-04 07:50:50 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-05-04 07:50:50 -0700
commitf4622045455faaac958ca35a0cf313f3d6c14d8b (patch)
tree96455f6f8a1afca46d939e9937913eb21782214b
parent0a6ba092d1c8c75ae0c0617ef7f4e6f5043af311 (diff)
parente419b4cc585680940bc42f8ca8a071d6023fb1bb (diff)
Merge branch 'fix-unmapped-word-at-a-time'
Jana Saout confirmed that this fixes the page faults he saw. His problem was triggered by ocfs2 and autofs symlink lookups, where the symlink allocation was at the end of a page. But the deeper reason seems to be the use of Xen-PV, which is what then causes him to have all these unmapped pages, which is what then makes it a problem when the unaligned word-at-a-time code fetches data past the end of a page. * fix-unmapped-word-at-a-time: vfs: make word-at-a-time accesses handle a non-existing page
-rw-r--r--arch/x86/Kconfig2
-rw-r--r--arch/x86/include/asm/word-at-a-time.h33
-rw-r--r--fs/dcache.c26
-rw-r--r--fs/namei.c4
4 files changed, 58 insertions, 7 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 1d14cc6b79ad..c9866b0b77d8 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -81,7 +81,7 @@ config X86
select CLKEVT_I8253
select ARCH_HAVE_NMI_SAFE_CMPXCHG
select GENERIC_IOMAP
- select DCACHE_WORD_ACCESS if !DEBUG_PAGEALLOC
+ select DCACHE_WORD_ACCESS
config INSTRUCTION_DECODER
def_bool (KPROBES || PERF_EVENTS)
diff --git a/arch/x86/include/asm/word-at-a-time.h b/arch/x86/include/asm/word-at-a-time.h
index 6fe6767b7124..e58f03b206c3 100644
--- a/arch/x86/include/asm/word-at-a-time.h
+++ b/arch/x86/include/asm/word-at-a-time.h
@@ -43,4 +43,37 @@ static inline unsigned long has_zero(unsigned long a)
return ((a - REPEAT_BYTE(0x01)) & ~a) & REPEAT_BYTE(0x80);
}
+/*
+ * Load an unaligned word from kernel space.
+ *
+ * In the (very unlikely) case of the word being a page-crosser
+ * and the next page not being mapped, take the exception and
+ * return zeroes in the non-existing part.
+ */
+static inline unsigned long load_unaligned_zeropad(const void *addr)
+{
+ unsigned long ret, dummy;
+
+ asm(
+ "1:\tmov %2,%0\n"
+ "2:\n"
+ ".section .fixup,\"ax\"\n"
+ "3:\t"
+ "lea %2,%1\n\t"
+ "and %3,%1\n\t"
+ "mov (%1),%0\n\t"
+ "leal %2,%%ecx\n\t"
+ "andl %4,%%ecx\n\t"
+ "shll $3,%%ecx\n\t"
+ "shr %%cl,%0\n\t"
+ "jmp 2b\n"
+ ".previous\n"
+ _ASM_EXTABLE(1b, 3b)
+ :"=&r" (ret),"=&c" (dummy)
+ :"m" (*(unsigned long *)addr),
+ "i" (-sizeof(unsigned long)),
+ "i" (sizeof(unsigned long)-1));
+ return ret;
+}
+
#endif /* _ASM_WORD_AT_A_TIME_H */
diff --git a/fs/dcache.c b/fs/dcache.c
index b60ddc41d783..b80531c91779 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -141,18 +141,29 @@ int proc_nr_dentry(ctl_table *table, int write, void __user *buffer,
* Compare 2 name strings, return 0 if they match, otherwise non-zero.
* The strings are both count bytes long, and count is non-zero.
*/
+#ifdef CONFIG_DCACHE_WORD_ACCESS
+
+#include <asm/word-at-a-time.h>
+/*
+ * NOTE! 'cs' and 'scount' come from a dentry, so it has a
+ * aligned allocation for this particular component. We don't
+ * strictly need the load_unaligned_zeropad() safety, but it
+ * doesn't hurt either.
+ *
+ * In contrast, 'ct' and 'tcount' can be from a pathname, and do
+ * need the careful unaligned handling.
+ */
static inline int dentry_cmp(const unsigned char *cs, size_t scount,
const unsigned char *ct, size_t tcount)
{
-#ifdef CONFIG_DCACHE_WORD_ACCESS
unsigned long a,b,mask;
if (unlikely(scount != tcount))
return 1;
for (;;) {
- a = *(unsigned long *)cs;
- b = *(unsigned long *)ct;
+ a = load_unaligned_zeropad(cs);
+ b = load_unaligned_zeropad(ct);
if (tcount < sizeof(unsigned long))
break;
if (unlikely(a != b))
@@ -165,7 +176,13 @@ static inline int dentry_cmp(const unsigned char *cs, size_t scount,
}
mask = ~(~0ul << tcount*8);
return unlikely(!!((a ^ b) & mask));
+}
+
#else
+
+static inline int dentry_cmp(const unsigned char *cs, size_t scount,
+ const unsigned char *ct, size_t tcount)
+{
if (scount != tcount)
return 1;
@@ -177,9 +194,10 @@ static inline int dentry_cmp(const unsigned char *cs, size_t scount,
tcount--;
} while (tcount);
return 0;
-#endif
}
+#endif
+
static void __d_free(struct rcu_head *head)
{
struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
diff --git a/fs/namei.c b/fs/namei.c
index 0062dd17eb55..c42791914f82 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1429,7 +1429,7 @@ unsigned int full_name_hash(const unsigned char *name, unsigned int len)
unsigned long hash = 0;
for (;;) {
- a = *(unsigned long *)name;
+ a = load_unaligned_zeropad(name);
if (len < sizeof(unsigned long))
break;
hash += a;
@@ -1459,7 +1459,7 @@ static inline unsigned long hash_name(const char *name, unsigned int *hashp)
do {
hash = (hash + a) * 9;
len += sizeof(unsigned long);
- a = *(unsigned long *)(name+len);
+ a = load_unaligned_zeropad(name+len);
/* Do we have any NUL or '/' bytes in this word? */
mask = has_zero(a) | has_zero(a ^ REPEAT_BYTE('/'));
} while (!mask);