[PATCH v4] tracing: remove igrab() iput() call from uprobes.c

From: Song Liu
Date: Fri Apr 20 2018 - 14:09:01 EST

Caller of uprobe_register is required to keep the inode and containing
mount point referenced.

There was misuse of igrab() in uprobes.c and trace_uprobe.c. This is
because igrab() will not prevent umount of the containing mount point.
To fix this, we added path to struct trace_uprobe, which keeps the inode
and containing mount reference.

For uprobes.c sisde, igrab() is not necessary. So we removed it and
added comments on requirements to callers of uprobe_register().

Link: http://lkml.kernel.org/r/CAELBmZB2XX=qEOLAdvGG4cPx4GEntcSnWQquJLUK1ongRj35cA@xxxxxxxxxxxxxx
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Howard McLauchlan <hmclauchlan@xxxxxx>
Cc: Josef Bacik <jbacik@xxxxxx>
Cc: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
Signed-off-by: Song Liu <songliubraving@xxxxxx>
kernel/events/uprobes.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index ce6848e..20486bb 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -491,7 +491,6 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
if (!uprobe)
return NULL;

- uprobe->inode = igrab(inode);
uprobe->offset = offset;
@@ -502,7 +501,6 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
if (cur_uprobe) {
uprobe = cur_uprobe;
- iput(inode);

return uprobe;
@@ -701,7 +699,6 @@ static void delete_uprobe(struct uprobe *uprobe)
rb_erase(&uprobe->rb_node, &uprobes_tree);
RB_CLEAR_NODE(&uprobe->rb_node); /* for uprobe_is_active() */
- iput(uprobe->inode);

@@ -873,7 +870,8 @@ static void __uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *u
* tuple). Creation refcount stops uprobe_unregister from freeing the
* @uprobe even before the register operation is complete. Creation
* refcount is released when the last @uc for the @uprobe
- * unregisters.
+ * unregisters. Caller of uprobe_register() is required to keep @inode
+ * (and the containing mount) referenced.
* Return errno if it cannot successully install probes
* else return 0 (success)