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x86/ioperm: Share I/O bitmap if identical

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The I/O bitmap is duplicated on fork. That's wasting memory and slows down
fork. There is no point to do so. As long as the bitmap is not modified it
can be shared between threads and processes.

Add a refcount and just share it on fork. If a task modifies the bitmap
then it has to do the duplication if and only if it is shared.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
This commit is contained in:
Thomas Gleixner
2019-11-11 23:03:25 +01:00
parent ea5f1cd7ab
commit 4804e382c1
3 changed files with 50 additions and 42 deletions
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39
arch/x86/kernel/process.c
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@@ -122,37 +122,13 @@ static int set_new_tls(struct task_struct *p, unsigned long tls)
return do_set_thread_area_64(p, ARCH_SET_FS, tls);
}
static inline int copy_io_bitmap(struct task_struct *tsk)
{
struct io_bitmap *iobm = current->thread.io_bitmap;
if (likely(!test_tsk_thread_flag(current, TIF_IO_BITMAP)))
return 0;
tsk->thread.io_bitmap = kmemdup(iobm, sizeof(*iobm), GFP_KERNEL);
if (!tsk->thread.io_bitmap)
return -ENOMEM;
set_tsk_thread_flag(tsk, TIF_IO_BITMAP);
return 0;
}
static inline void free_io_bitmap(struct task_struct *tsk)
{
if (tsk->thread.io_bitmap) {
kfree(tsk->thread.io_bitmap);
tsk->thread.io_bitmap = NULL;
}
}
int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
unsigned long arg, struct task_struct *p, unsigned long tls)
{
struct inactive_task_frame *frame;
struct fork_frame *fork_frame;
struct pt_regs *childregs;
int ret;
int ret = 0;
childregs = task_pt_regs(p);
fork_frame = container_of(childregs, struct fork_frame, regs);
@@ -199,16 +175,13 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
task_user_gs(p) = get_user_gs(current_pt_regs());
#endif
ret = copy_io_bitmap(p);
if (ret)
return ret;
/* Set a new TLS for the child thread? */
if (clone_flags & CLONE_SETTLS) {
if (clone_flags & CLONE_SETTLS)
ret = set_new_tls(p, tls);
if (ret)
free_io_bitmap(p);
}
if (!ret && unlikely(test_tsk_thread_flag(current, TIF_IO_BITMAP)))
io_bitmap_share(p);
return ret;
}