alignment faults in 3.6
Russell King - ARM Linux
linux at arm.linux.org.uk
Fri Oct 5 06:51:33 EDT 2012
On Fri, Oct 05, 2012 at 08:29:14AM +0100, Russell King - ARM Linux wrote:
> On Thu, Oct 04, 2012 at 06:10:26PM -0500, Rob Herring wrote:
> > I would think the scheduling while atomic messages are harmless in this
> > case. However, in addition to spewing out BUG messages this commit also
> > seems to eventually cause a kernel panic in __napi_complete. That panic
> > seems to go away if I put barrier() between the 2 accesses above which
> > eliminates the alignment faults. I haven't figured that part out yet.
> >
> > There's at least a couple of problems here:
> >
> > This seems like an overly aggressive compiler optimization considering
> > unaligned accesses are not supported by ldm/stm.
> >
> > The alignment fault handler should handle kernel address faults atomically.
>
> This is bad news. do_alignment() can be called in almost any kernel
> context, and it must work. die() and oops dumps - specifically dump_mem()
> and dump_instr() will suffer from exactly the same problem.
Okay, this should fix the issue... I've only compile tested it so far.
Rob, as you have a way to trigger this easily, can you give this patch
a go and let me know if it solves your problem? Thanks.
arch/arm/kernel/traps.c | 34 +++++++---------------------------
arch/arm/mm/alignment.c | 11 ++++-------
2 files changed, 11 insertions(+), 34 deletions(-)
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index b0179b8..62f429e 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -89,17 +89,8 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
unsigned long top)
{
unsigned long first;
- mm_segment_t fs;
int i;
- /*
- * We need to switch to kernel mode so that we can use __get_user
- * to safely read from kernel space. Note that we now dump the
- * code first, just in case the backtrace kills us.
- */
- fs = get_fs();
- set_fs(KERNEL_DS);
-
printk("%s%s(0x%08lx to 0x%08lx)\n", lvl, str, bottom, top);
for (first = bottom & ~31; first < top; first += 32) {
@@ -112,7 +103,7 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
for (p = first, i = 0; i < 8 && p < top; i++, p += 4) {
if (p >= bottom && p < top) {
unsigned long val;
- if (__get_user(val, (unsigned long *)p) == 0)
+ if (probe_kernel_address(p, val) == 0)
sprintf(str + i * 9, " %08lx", val);
else
sprintf(str + i * 9, " ????????");
@@ -120,8 +111,6 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom,
}
printk("%s%04lx:%s\n", lvl, first & 0xffff, str);
}
-
- set_fs(fs);
}
static void dump_instr(const char *lvl, struct pt_regs *regs)
@@ -129,25 +118,18 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
unsigned long addr = instruction_pointer(regs);
const int thumb = thumb_mode(regs);
const int width = thumb ? 4 : 8;
- mm_segment_t fs;
char str[sizeof("00000000 ") * 5 + 2 + 1], *p = str;
int i;
- /*
- * We need to switch to kernel mode so that we can use __get_user
- * to safely read from kernel space. Note that we now dump the
- * code first, just in case the backtrace kills us.
- */
- fs = get_fs();
- set_fs(KERNEL_DS);
-
for (i = -4; i < 1 + !!thumb; i++) {
unsigned int val, bad;
- if (thumb)
- bad = __get_user(val, &((u16 *)addr)[i]);
- else
- bad = __get_user(val, &((u32 *)addr)[i]);
+ if (thumb) {
+ u16 instr;
+ bad = probe_kernel_address(addr, instr);
+ val = instr;
+ } else
+ bad = probe_kernel_address(addr, val);
if (!bad)
p += sprintf(p, i == 0 ? "(%0*x) " : "%0*x ",
@@ -158,8 +140,6 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
}
}
printk("%sCode: %s\n", lvl, str);
-
- set_fs(fs);
}
#ifdef CONFIG_ARM_UNWIND
diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c
index b9f60eb..f8f14fc 100644
--- a/arch/arm/mm/alignment.c
+++ b/arch/arm/mm/alignment.c
@@ -749,7 +749,6 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
unsigned long instr = 0, instrptr;
int (*handler)(unsigned long addr, unsigned long instr, struct pt_regs *regs);
unsigned int type;
- mm_segment_t fs;
unsigned int fault;
u16 tinstr = 0;
int isize = 4;
@@ -760,16 +759,15 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
instrptr = instruction_pointer(regs);
- fs = get_fs();
- set_fs(KERNEL_DS);
if (thumb_mode(regs)) {
- fault = __get_user(tinstr, (u16 *)(instrptr & ~1));
+ unsigned long ptr = instrptr;
+ fault = probe_kernel_address(ptr, tinstr);
if (!fault) {
if (cpu_architecture() >= CPU_ARCH_ARMv7 &&
IS_T32(tinstr)) {
/* Thumb-2 32-bit */
u16 tinst2 = 0;
- fault = __get_user(tinst2, (u16 *)(instrptr+2));
+ fault = probe_kernel_address(ptr + 2, tinst2);
instr = (tinstr << 16) | tinst2;
thumb2_32b = 1;
} else {
@@ -778,8 +776,7 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
}
}
} else
- fault = __get_user(instr, (u32 *)instrptr);
- set_fs(fs);
+ fault = probe_kernel_address(instrptr, instr);
if (fault) {
type = TYPE_FAULT;
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