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Subject[PATCH 4/5] uprobes: teach set_xol_ip() to use uprobe_xol_slots[]
Change set_xol_ip() to use uprobe_xol_slots[] per-cpu array to
"allocate" the insn slot. We do not care if the task migrates to
another CPU before executing xol insn, set_xol_ip() will be called
again by uprobe_switch_to(). Likewise, we do not care if the task
is simply preempted or sleeps.

IOW, uprobe_xol_slots[CPU] is "owned" by cpu_curr(CPU).

This makes xol_get_insn_slot/xol_free_insn_slot unnecessary, but
uprobe_notify_resume() should set utask->vaddr. The patch updates
the callers but doesn't remove this code to simplify the review.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/uprobes.c | 16 ++++++++++------
1 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/kernel/uprobes.c b/kernel/uprobes.c
index 20007da..c9e2f65 100644
--- a/kernel/uprobes.c
+++ b/kernel/uprobes.c
@@ -1285,7 +1285,6 @@ void free_uprobe_utask(struct task_struct *tsk)
if (utask->active_uprobe)
put_uprobe(utask->active_uprobe);

- xol_free_insn_slot(tsk);
kfree(utask);
tsk->utask = NULL;
}
@@ -1347,7 +1346,15 @@ uprobe_xol_slots[UPROBES_XOL_SLOT_BYTES][NR_CPUS] __page_aligned_bss;

void __weak set_xol_ip(struct pt_regs *regs)
{
- set_instruction_pointer(regs, current->utask->xol_vaddr);
+ int cpu = smp_processor_id();
+ struct uprobe_task *utask = current->utask;
+ struct uprobe *uprobe = utask->active_uprobe;
+
+ memcpy(uprobe_xol_slots[cpu], uprobe->insn, MAX_UINSN_BYTES);
+
+ utask->xol_vaddr = fix_to_virt(UPROBE_XOL_FIRST_PAGE)
+ + UPROBES_XOL_SLOT_BYTES * cpu;
+ set_instruction_pointer(regs, utask->xol_vaddr);
}

/*
@@ -1390,14 +1397,12 @@ void uprobe_notify_resume(struct pt_regs *regs)
goto cleanup_ret;
}
utask->active_uprobe = u;
+ utask->vaddr = probept;
handler_chain(u, regs);

if (u->flags & UPROBES_SKIP_SSTEP && can_skip_xol(regs, u))
goto cleanup_ret;

- if (!xol_get_insn_slot(u, probept))
- goto cleanup_ret;
-
if (pre_xol(u, regs))
goto cleanup_ret;

@@ -1419,7 +1424,6 @@ void uprobe_notify_resume(struct pt_regs *regs)
utask->active_uprobe = NULL;
utask->state = UTASK_RUNNING;
user_disable_single_step(current);
- xol_free_insn_slot(current);

spin_lock_irq(&current->sighand->siglock);
recalc_sigpending(); /* see uprobe_deny_signal() */
--
1.5.5.1



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