Hello,
I would like to follow-up the TIF flags and especially on the
rules of inheritance. It appears the TIF flags are copied from
parent to child task systematically on copy_process.
Then they are adjusted in copy_threads() or sub-functions.
The TIF_IO_BITMAP is checked in copy_threads() with the following code:
int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
unsigned long unused,
struct task_struct * p, struct pt_regs * regs)
{
....
if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
if (!p->thread.io_bitmap_ptr) {
p->thread.io_bitmap_max = 0;
return -ENOMEM;
}
memcpy(p->thread.io_bitmap_ptr, tsk->thread.io_bitmap_ptr,
IO_BITMAP_BYTES);
set_tsk_thread_flag(p, TIF_IO_BITMAP);
}
I would think that the set_tsk_thread_flag() is extraneous.
As for TIF_DEBUG, my patch is not clearing it. I don't think you can
have HW breakpoints be inherited from one task to the other.
Any comments on this?
On Wed, Jul 05, 2006 at 04:54:06AM -0700, Stephane Eranian wrote:
> Hello,
>
> Here is the second version of my TIF flag patch for i386.
> This version incoporates the changes suggested by Chuck.
>
> This patch is against mainline.
>
> This patch covers the i386 modifications.
>
> Changelog:
> - add TIF_DEBUG to track when debug registers are active
> - add TIF_IO_BITMAP to track when I/O bitmap is used
> - modify __switch_to() to use the new TIF flags
>
> <signed-off-by>: [email protected]
>
> diff --git a/arch/i386/kernel/ioport.c b/arch/i386/kernel/ioport.c
> --- a/arch/i386/kernel/ioport.c
> +++ b/arch/i386/kernel/ioport.c
> @@ -79,6 +79,7 @@ asmlinkage long sys_ioperm(unsigned long
>
> memset(bitmap, 0xff, IO_BITMAP_BYTES);
> t->io_bitmap_ptr = bitmap;
> + set_thread_flag(TIF_IO_BITMAP);
> }
>
> /*
> diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
> --- a/arch/i386/kernel/process.c
> +++ b/arch/i386/kernel/process.c
> @@ -359,16 +359,16 @@ EXPORT_SYMBOL(kernel_thread);
> */
> void exit_thread(void)
> {
> - struct task_struct *tsk = current;
> - struct thread_struct *t = &tsk->thread;
> -
> /* The process may have allocated an io port bitmap... nuke it. */
> - if (unlikely(NULL != t->io_bitmap_ptr)) {
> + if (unlikely(test_thread_flag(TIF_IO_BITMAP))) {
> + struct task_struct *tsk = current;
> + struct thread_struct *t = &tsk->thread;
> int cpu = get_cpu();
> struct tss_struct *tss = &per_cpu(init_tss, cpu);
>
> kfree(t->io_bitmap_ptr);
> t->io_bitmap_ptr = NULL;
> + clear_thread_flag(TIF_IO_BITMAP);
> /*
> * Careful, clear this in the TSS too:
> */
> @@ -387,6 +387,7 @@ void flush_thread(void)
>
> memset(tsk->thread.debugreg, 0, sizeof(unsigned long)*8);
> memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
> + clear_tsk_thread_flag(tsk, TIF_DEBUG);
> /*
> * Forget coprocessor state..
> */
> @@ -431,7 +432,7 @@ int copy_thread(int nr, unsigned long cl
> savesegment(gs,p->thread.gs);
>
> tsk = current;
> - if (unlikely(NULL != tsk->thread.io_bitmap_ptr)) {
> + if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
> p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
> if (!p->thread.io_bitmap_ptr) {
> p->thread.io_bitmap_max = 0;
> @@ -439,6 +440,7 @@ int copy_thread(int nr, unsigned long cl
> }
> memcpy(p->thread.io_bitmap_ptr, tsk->thread.io_bitmap_ptr,
> IO_BITMAP_BYTES);
> + set_tsk_thread_flag(p, TIF_IO_BITMAP);
> }
>
> /*
> @@ -533,10 +535,24 @@ int dump_task_regs(struct task_struct *t
> return 1;
> }
>
> -static inline void
> -handle_io_bitmap(struct thread_struct *next, struct tss_struct *tss)
> +static inline void __switch_to_xtra(struct task_struct *next_p,
> + struct tss_struct *tss)
> {
> - if (!next->io_bitmap_ptr) {
> + struct thread_struct *next;
> +
> + next = &next_p->thread;
> +
> + if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
> + set_debugreg(next->debugreg[0], 0);
> + set_debugreg(next->debugreg[1], 1);
> + set_debugreg(next->debugreg[2], 2);
> + set_debugreg(next->debugreg[3], 3);
> + /* no 4 and 5 */
> + set_debugreg(next->debugreg[6], 6);
> + set_debugreg(next->debugreg[7], 7);
> + }
> +
> + if (!test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
> /*
> * Disable the bitmap via an invalid offset. We still cache
> * the previous bitmap owner and the IO bitmap contents:
> @@ -544,6 +560,7 @@ handle_io_bitmap(struct thread_struct *n
> tss->io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
> return;
> }
> +
> if (likely(next == tss->io_bitmap_owner)) {
> /*
> * Previous owner of the bitmap (hence the bitmap content)
> @@ -673,18 +690,9 @@ struct task_struct fastcall * __switch_t
> /*
> * Now maybe reload the debug registers
> */
> - if (unlikely(next->debugreg[7])) {
> - set_debugreg(next->debugreg[0], 0);
> - set_debugreg(next->debugreg[1], 1);
> - set_debugreg(next->debugreg[2], 2);
> - set_debugreg(next->debugreg[3], 3);
> - /* no 4 and 5 */
> - set_debugreg(next->debugreg[6], 6);
> - set_debugreg(next->debugreg[7], 7);
> - }
> -
> - if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr))
> - handle_io_bitmap(next, tss);
> + if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW))
> + || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP))
> + __switch_to_xtra(next_p, tss);
>
> disable_tsc(prev_p, next_p);
>
> diff --git a/arch/i386/kernel/ptrace.c b/arch/i386/kernel/ptrace.c
> --- a/arch/i386/kernel/ptrace.c
> +++ b/arch/i386/kernel/ptrace.c
> @@ -468,8 +468,11 @@ long arch_ptrace(struct task_struct *chi
> for(i=0; i<4; i++)
> if ((0x5f54 >> ((data >> (16 + 4*i)) & 0xf)) & 1)
> goto out_tsk;
> + if (data)
> + set_tsk_thread_flag(child, TIF_DEBUG);
> + else
> + clear_tsk_thread_flag(child, TIF_DEBUG);
> }
> -
> addr -= (long) &dummy->u_debugreg;
> addr = addr >> 2;
> child->thread.debugreg[addr] = data;
> diff --git a/include/asm-i386/thread_info.h b/include/asm-i386/thread_info.h
> --- a/include/asm-i386/thread_info.h
> +++ b/include/asm-i386/thread_info.h
> @@ -140,6 +140,8 @@ static inline struct thread_info *curren
> #define TIF_SECCOMP 8 /* secure computing */
> #define TIF_RESTORE_SIGMASK 9 /* restore signal mask in do_signal() */
> #define TIF_MEMDIE 16
> +#define TIF_DEBUG 17 /* uses debug registers */
> +#define TIF_IO_BITMAP 18 /* uses I/O bitmap */
>
> #define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE)
> #define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME)
> @@ -151,6 +153,8 @@ static inline struct thread_info *curren
> #define _TIF_SYSCALL_AUDIT (1<<TIF_SYSCALL_AUDIT)
> #define _TIF_SECCOMP (1<<TIF_SECCOMP)
> #define _TIF_RESTORE_SIGMASK (1<<TIF_RESTORE_SIGMASK)
> +#define _TIF_DEBUG (1<<TIF_DEBUG)
> +#define _TIF_IO_BITMAP (1<<TIF_IO_BITMAP)
>
> /* work to do on interrupt/exception return */
> #define _TIF_WORK_MASK \
> @@ -159,6 +163,9 @@ static inline struct thread_info *curren
> /* work to do on any return to u-space */
> #define _TIF_ALLWORK_MASK (0x0000FFFF & ~_TIF_SECCOMP)
>
> +/* flags to check in __switch_to() */
> +#define _TIF_WORK_CTXSW (_TIF_DEBUG|_TIF_IO_BITMAP)
> +
> /*
> * Thread-synchronous status.
> *
--
-Stephane
-
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