Messages in this thread Patch in this message | | | Date | Wed, 6 Jun 2012 08:12:40 -0700 | From | tip-bot for Oleg Nesterov <> | Subject | [tip:perf/core] uprobes: Teach handle_swbp() to rely on %22is_swbp%22 rather than uprobes_srcu |
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Commit-ID: 27e471e0846354376d180c2d2911ec9b94f1e28f Gitweb: http://git.kernel.org/tip/27e471e0846354376d180c2d2911ec9b94f1e28f Author: Oleg Nesterov <oleg@redhat.com> AuthorDate: Tue, 29 May 2012 21:29:47 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Wed, 6 Jun 2012 11:30:57 +0200
uprobes: Teach handle_swbp() to rely on %22is_swbp%22 rather than uprobes_srcu
Currently handle_swbp() assumes that it can't race with unregister, so it roughly does:
if (find_uprobe(vaddr)) process_uprobe(); else send_sig(SIGTRAP);
This relies on the not-really-working uprobes_srcu code we are going to remove, see the next patch.
With this patch we rely on the result of is_swbp_at_addr(bp_vaddr) if find_uprobe() fails.
If is_swbp == 1, then we hit the normal int3, we should send SIGTRAP.
If is_swbp == 0, we raced with uprobe_unregister(), we simply restart this insn again.
The "difficult" case is is_swbp == -EFAULT, when we can't read this memory. In this case I think we should restart too, and this is more correct compared to the current code which sends SIGTRAP.
Ignoring ENOMEM/etc from get_user_pages(), this can only happen if another thread unmaps this memory before find_active_uprobe() takes mmap_sem. It would be better to pretend it was unmapped before this insn was executed, restart, and get SIGSEGV.
Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com> Cc: Anton Arapov <anton@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20120529192947.GF8057@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org> --- kernel/events/uprobes.c | 18 +++++++++++++++--- 1 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index a2ed82b..1f02e3b 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -1530,14 +1530,26 @@ static void handle_swbp(struct pt_regs *regs) struct uprobe_task *utask; struct uprobe *uprobe; unsigned long bp_vaddr; - int is_swbp; + int uninitialized_var(is_swbp); bp_vaddr = uprobe_get_swbp_addr(regs); uprobe = find_active_uprobe(bp_vaddr, &is_swbp); if (!uprobe) { - /* No matching uprobe; signal SIGTRAP. */ - send_sig(SIGTRAP, current, 0); + if (is_swbp > 0) { + /* No matching uprobe; signal SIGTRAP. */ + send_sig(SIGTRAP, current, 0); + } else { + /* + * Either we raced with uprobe_unregister() or we can't + * access this memory. The latter is only possible if + * another thread plays with our ->mm. In both cases + * we can simply restart. If this vma was unmapped we + * can pretend this insn was not executed yet and get + * the (correct) SIGSEGV after restart. + */ + instruction_pointer_set(regs, bp_vaddr); + } return; }
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