uprobes: Allocate ->utask before handler_chain() for tracing handlers

uprobe_trace_print() and uprobe_perf_print() need to pass the additional
info to call_fetch() methods, currently there is no simple way to do this.

current->utask looks like a natural place to hold this info, but we need
to allocate it before handler_chain().

This is a bit unfortunate, perhaps we will find a better solution later,
but this is simple and should work right now.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 24b7d6ca871b..3cc8e0bb8acf 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1828,6 +1828,10 @@ static void handle_swbp(struct pt_regs *regs)
         if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags)))
                 goto out;
 
+        /* Tracing handlers use ->utask to communicate with fetch methods */
+        if (!get_utask())
+                goto out;
+
         handler_chain(uprobe, regs);
         if (can_skip_sstep(uprobe, regs))
                 goto out;