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arch/tile: fix up some issues in calling do_work_pending()

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First, we were at risk of handling thread-info flags, in particular
do_signal(), when returning from kernel space.  This could happen
after a failed kernel_execve(), or when forking a kernel thread.
The fix is to test in do_work_pending() for user_mode() and return
immediately if so; we already had this test for one of the flags,
so I just hoisted it to the top of the function.

Second, if a ptraced process updated the callee-saved registers
in the ptregs struct and then processed another thread-info flag, we
would overwrite the modifications with the original callee-saved
registers.  To fix this, we add a register to note if we've already
saved the registers once, and skip doing it on additional passes
through the loop.  To avoid a performance hit from the couple of
extra instructions involved, I modified the GET_THREAD_INFO() macro
to be guaranteed to be one instruction, then bundled it with adjacent
instructions, yielding an overall net savings.

Reported-By: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
This commit is contained in:
Chris Metcalf 2012-04-28 18:51:43 -04:00
parent 36be50515f
commit fc327e268f
4 changed files with 68 additions and 27 deletions
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9
arch/tile/include/asm/thread_info.h
View file

@ -100,9 +100,14 @@ extern void cpu_idle_on_new_stack(struct thread_info *old_ti,
#else /* __ASSEMBLY__ */
/* how to get the thread information struct from ASM */
/*
* How to get the thread information struct from assembly.
* Note that we use different macros since different architectures
* have different semantics in their "mm" instruction and we would
* like to guarantee that the macro expands to exactly one instruction.
*/
#ifdef __tilegx__
#define GET_THREAD_INFO(reg) move reg, sp; mm reg, zero, LOG2_THREAD_SIZE, 63
#define EXTRACT_THREAD_INFO(reg) mm reg, zero, LOG2_THREAD_SIZE, 63
#else
#define GET_THREAD_INFO(reg) mm reg, sp, zero, LOG2_THREAD_SIZE, 31
#endif

41
arch/tile/kernel/intvec_32.S
View file

@ -838,6 +838,18 @@ STD_ENTRY(interrupt_return)
.Lresume_userspace:
FEEDBACK_REENTER(interrupt_return)
/*
* Use r33 to hold whether we have already loaded the callee-saves
* into ptregs. We don't want to do it twice in this loop, since
* then we'd clobber whatever changes are made by ptrace, etc.
* Get base of stack in r32.
*/
{
GET_THREAD_INFO(r32)
movei r33, 0
}
.Lretry_work_pending:
/*
* Disable interrupts so as to make sure we don't
* miss an interrupt that sets any of the thread flags (like
@ -848,9 +860,6 @@ STD_ENTRY(interrupt_return)
IRQ_DISABLE(r20, r21)
TRACE_IRQS_OFF /* Note: clobbers registers r0-r29 */
/* Get base of stack in r32; note r30/31 are used as arguments here. */
GET_THREAD_INFO(r32)
/* Check to see if there is any work to do before returning to user. */
{
@ -866,16 +875,18 @@ STD_ENTRY(interrupt_return)
/*
* Make sure we have all the registers saved for signal
* handling or single-step. Call out to C code to figure out
* exactly what we need to do for each flag bit, then if
* necessary, reload the flags and recheck.
* handling, notify-resume, or single-step. Call out to C
* code to figure out exactly what we need to do for each flag bit,
* then if necessary, reload the flags and recheck.
*/
push_extra_callee_saves r0
{
PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
jal do_work_pending
bnz r33, 1f
}
bnz r0, .Lresume_userspace
push_extra_callee_saves r0
movei r33, 1
1: jal do_work_pending
bnz r0, .Lretry_work_pending
/*
* In the NMI case we
@ -1180,10 +1191,12 @@ handle_syscall:
add r20, r20, tp
lw r21, r20
addi r21, r21, 1
sw r20, r21
{
sw r20, r21
GET_THREAD_INFO(r31)
}
/* Trace syscalls, if requested. */
GET_THREAD_INFO(r31)
addi r31, r31, THREAD_INFO_FLAGS_OFFSET
lw r30, r31
andi r30, r30, _TIF_SYSCALL_TRACE
@ -1362,7 +1375,10 @@ handle_ill:
3:
/* set PC and continue */
lw r26, r24
sw r28, r26
{
sw r28, r26
GET_THREAD_INFO(r0)
}
/*
* Clear TIF_SINGLESTEP to prevent recursion if we execute an ill.
@ -1370,7 +1386,6 @@ handle_ill:
* need to clear it here and can't really impose on all other arches.
* So what's another write between friends?
*/
GET_THREAD_INFO(r0)
addi r1, r0, THREAD_INFO_FLAGS_OFFSET
{

38
arch/tile/kernel/intvec_64.S
View file

@ -646,6 +646,20 @@ STD_ENTRY(interrupt_return)
.Lresume_userspace:
FEEDBACK_REENTER(interrupt_return)
/*
* Use r33 to hold whether we have already loaded the callee-saves
* into ptregs. We don't want to do it twice in this loop, since
* then we'd clobber whatever changes are made by ptrace, etc.
*/
{
movei r33, 0
move r32, sp
}
/* Get base of stack in r32. */
EXTRACT_THREAD_INFO(r32)
.Lretry_work_pending:
/*
* Disable interrupts so as to make sure we don't
* miss an interrupt that sets any of the thread flags (like
@ -656,9 +670,6 @@ STD_ENTRY(interrupt_return)
IRQ_DISABLE(r20, r21)
TRACE_IRQS_OFF /* Note: clobbers registers r0-r29 */
/* Get base of stack in r32; note r30/31 are used as arguments here. */
GET_THREAD_INFO(r32)
/* Check to see if there is any work to do before returning to user. */
{
@ -674,16 +685,18 @@ STD_ENTRY(interrupt_return)
/*
* Make sure we have all the registers saved for signal
* handling or single-step. Call out to C code to figure out
* handling or notify-resume. Call out to C code to figure out
* exactly what we need to do for each flag bit, then if
* necessary, reload the flags and recheck.
*/
push_extra_callee_saves r0
{
PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
jal do_work_pending
bnez r33, 1f
}
bnez r0, .Lresume_userspace
push_extra_callee_saves r0
movei r33, 1
1: jal do_work_pending
bnez r0, .Lretry_work_pending
/*
* In the NMI case we
@ -968,11 +981,16 @@ handle_syscall:
shl16insli r20, r20, hw0(irq_stat + IRQ_CPUSTAT_SYSCALL_COUNT_OFFSET)
add r20, r20, tp
ld4s r21, r20
addi r21, r21, 1
st4 r20, r21
{
addi r21, r21, 1
move r31, sp
}
{
st4 r20, r21
EXTRACT_THREAD_INFO(r31)
}
/* Trace syscalls, if requested. */
GET_THREAD_INFO(r31)
addi r31, r31, THREAD_INFO_FLAGS_OFFSET
ld r30, r31
andi r30, r30, _TIF_SYSCALL_TRACE

7
arch/tile/kernel/process.c
View file

@ -567,6 +567,10 @@ struct task_struct *__sched _switch_to(struct task_struct *prev,
*/
int do_work_pending(struct pt_regs *regs, u32 thread_info_flags)
{
/* If we enter in kernel mode, do nothing and exit the caller loop. */
if (!user_mode(regs))
return 0;
if (thread_info_flags & _TIF_NEED_RESCHED) {
schedule();
return 1;
@ -589,8 +593,7 @@ int do_work_pending(struct pt_regs *regs, u32 thread_info_flags)
return 1;
}
if (thread_info_flags & _TIF_SINGLESTEP) {
if ((regs->ex1 & SPR_EX_CONTEXT_1_1__PL_MASK) == 0)
single_step_once(regs);
single_step_once(regs);
return 0;
}
panic("work_pending: bad flags %#x\n", thread_info_flags);