From: Song Liu songliubraving@fb.com

As Miklos reported and suggested:

This pattern repeats two times in trace_uprobe.c and in kernel/events/core.c as well:

ret = kern_path(filename, LOOKUP_FOLLOW, &path); if (ret) goto fail_address_parse;

inode = igrab(d_inode(path.dentry)); path_put(&path);

And it's wrong. You can only hold a reference to the inode if you have an active ref to the superblock as well (which is normally through path.mnt) or holding s_umount.

This way unmounting the containing filesystem while the tracepoint is active will give you the "VFS: Busy inodes after unmount..." message and a crash when the inode is finally put.

Solution: store path instead of inode.

This patch fixes two instances in trace_uprobe.c. struct path is added to struct trace_uprobe to keep the inode and containing mount point referenced.

Link: http://lkml.kernel.org/r/20180423172135.4050588-1-songliubraving@fb.com

Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes") Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU") Cc: stable@vger.kernel.org Cc: Ingo Molnar mingo@redhat.com Cc: Howard McLauchlan hmclauchlan@fb.com Cc: Josef Bacik jbacik@fb.com Cc: Srikar Dronamraju srikar@linux.vnet.ibm.com Acked-by: Miklos Szeredi mszeredi@redhat.com Reported-by: Miklos Szeredi miklos@szeredi.hu Signed-off-by: Song Liu songliubraving@fb.com Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org --- kernel/trace/trace_uprobe.c | 35 ++++++++++++++--------------------- 1 file changed, 14 insertions(+), 21 deletions(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c index 34fd0e0ec51d..ac892878dbe6 100644 --- a/kernel/trace/trace_uprobe.c +++ b/kernel/trace/trace_uprobe.c @@ -55,6 +55,7 @@ struct trace_uprobe { struct list_head list; struct trace_uprobe_filter filter; struct uprobe_consumer consumer; + struct path path; struct inode *inode; char *filename; unsigned long offset; @@ -289,7 +290,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu) for (i = 0; i < tu->tp.nr_args; i++) traceprobe_free_probe_arg(&tu->tp.args[i]);

- iput(tu->inode); + path_put(&tu->path); kfree(tu->tp.call.class->system); kfree(tu->tp.call.name); kfree(tu->filename); @@ -363,7 +364,6 @@ static int register_trace_uprobe(struct trace_uprobe *tu) static int create_trace_uprobe(int argc, char **argv) { struct trace_uprobe *tu; - struct inode *inode; char *arg, *event, *group, *filename; char buf[MAX_EVENT_NAME_LEN]; struct path path; @@ -371,7 +371,6 @@ static int create_trace_uprobe(int argc, char **argv) bool is_delete, is_return; int i, ret;

- inode = NULL; ret = 0; is_delete = false; is_return = false; @@ -437,21 +436,16 @@ static int create_trace_uprobe(int argc, char **argv) } /* Find the last occurrence, in case the path contains ':' too. */ arg = strrchr(argv[1], ':'); - if (!arg) { - ret = -EINVAL; - goto fail_address_parse; - } + if (!arg) + return -EINVAL;

*arg++ = '\0'; filename = argv[1]; ret = kern_path(filename, LOOKUP_FOLLOW, &path); if (ret) - goto fail_address_parse; - - inode = igrab(d_real_inode(path.dentry)); - path_put(&path); + return ret;

- if (!inode || !S_ISREG(inode->i_mode)) { + if (!d_is_reg(path.dentry)) { ret = -EINVAL; goto fail_address_parse; } @@ -490,7 +484,7 @@ static int create_trace_uprobe(int argc, char **argv) goto fail_address_parse; } tu->offset = offset; - tu->inode = inode; + tu->path = path; tu->filename = kstrdup(filename, GFP_KERNEL);

if (!tu->filename) { @@ -558,7 +552,7 @@ static int create_trace_uprobe(int argc, char **argv) return ret;

fail_address_parse: - iput(inode); + path_put(&path);

pr_info("Failed to parse address or file.\n");

@@ -922,6 +916,7 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file, goto err_flags;

tu->consumer.filter = filter; + tu->inode = d_real_inode(tu->path.dentry); ret = uprobe_register(tu->inode, tu->offset, &tu->consumer); if (ret) goto err_buffer; @@ -967,6 +962,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file) WARN_ON(!uprobe_filter_is_empty(&tu->filter));

uprobe_unregister(tu->inode, tu->offset, &tu->consumer); + tu->inode = NULL; tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;

uprobe_buffer_disable(); @@ -1337,7 +1333,6 @@ struct trace_event_call * create_local_trace_uprobe(char *name, unsigned long offs, bool is_return) { struct trace_uprobe *tu; - struct inode *inode; struct path path; int ret;

@@ -1345,11 +1340,8 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return) if (ret) return ERR_PTR(ret);

- inode = igrab(d_inode(path.dentry)); - path_put(&path); - - if (!inode || !S_ISREG(inode->i_mode)) { - iput(inode); + if (!d_is_reg(path.dentry)) { + path_put(&path); return ERR_PTR(-EINVAL); }

@@ -1364,11 +1356,12 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return) if (IS_ERR(tu)) { pr_info("Failed to allocate trace_uprobe.(%d)\n", (int)PTR_ERR(tu)); + path_put(&path); return ERR_CAST(tu); }

tu->offset = offs; - tu->inode = inode; + tu->path = path; tu->filename = kstrdup(name, GFP_KERNEL); init_trace_event_call(tu, &tu->tp.call);