linux-kernel - [PATCH] binder: fix log spam for existing debugfs file creation.

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Date:   Fri, 10 Jan 2020 16:44:01 +0100
From:   Martin Fuzzey <martin.fuzzey@...wbird.group>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <christian@...uner.io>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: [PATCH] binder: fix log spam for existing debugfs file creation.

Since commit 43e23b6c0b01 ("debugfs: log errors when something goes wrong")
debugfs logs attempts to create existing files.

However binder attempts to create multiple debugfs files with
the same name when a single PID has multiple contexts, this leads
to log spamming during an Android boot (17 such messages during
boot on my system).

Fix this by checking if we already know the PID and only create
the debugfs entry for the first context per PID.

Do the same thing for binderfs for symmetry.

Signed-off-by: Martin Fuzzey <martin.fuzzey@...wbird.group>
---
 drivers/android/binder.c | 37 +++++++++++++++++++------------------
 1 file changed, 19 insertions(+), 18 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 976a694..254f87b 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -5203,10 +5203,11 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
 
 static int binder_open(struct inode *nodp, struct file *filp)
 {
-	struct binder_proc *proc;
+	struct binder_proc *proc, *itr;
 	struct binder_device *binder_dev;
 	struct binderfs_info *info;
 	struct dentry *binder_binderfs_dir_entry_proc = NULL;
+	bool existing_pid = false;
 
 	binder_debug(BINDER_DEBUG_OPEN_CLOSE, "%s: %d:%d\n", __func__,
 		     current->group_leader->pid, current->pid);
@@ -5239,19 +5240,24 @@ static int binder_open(struct inode *nodp, struct file *filp)
 	filp->private_data = proc;
 
 	mutex_lock(&binder_procs_lock);
+	hlist_for_each_entry(itr, &binder_procs, proc_node) {
+		if (itr->pid == proc->pid) {
+			existing_pid = true;
+			break;
+		}
+	}
 	hlist_add_head(&proc->proc_node, &binder_procs);
 	mutex_unlock(&binder_procs_lock);
 
-	if (binder_debugfs_dir_entry_proc) {
+	if (binder_debugfs_dir_entry_proc && !existing_pid) {
 		char strbuf[11];
 
 		snprintf(strbuf, sizeof(strbuf), "%u", proc->pid);
 		/*
-		 * proc debug entries are shared between contexts, so
-		 * this will fail if the process tries to open the driver
-		 * again with a different context. The priting code will
-		 * anyway print all contexts that a given PID has, so this
-		 * is not a problem.
+		 * proc debug entries are shared between contexts.
+		 * Only create for the first PID to avoid debugfs log spamming
+		 * The printing code will anyway print all contexts for a given
+		 * PID so this is not a problem.
 		 */
 		proc->debugfs_entry = debugfs_create_file(strbuf, 0444,
 			binder_debugfs_dir_entry_proc,
@@ -5259,19 +5265,16 @@ static int binder_open(struct inode *nodp, struct file *filp)
 			&proc_fops);
 	}
 
-	if (binder_binderfs_dir_entry_proc) {
+	if (binder_binderfs_dir_entry_proc && !existing_pid) {
 		char strbuf[11];
 		struct dentry *binderfs_entry;
 
 		snprintf(strbuf, sizeof(strbuf), "%u", proc->pid);
 		/*
 		 * Similar to debugfs, the process specific log file is shared
-		 * between contexts. If the file has already been created for a
-		 * process, the following binderfs_create_file() call will
-		 * fail with error code EEXIST if another context of the same
-		 * process invoked binder_open(). This is ok since same as
-		 * debugfs, the log file will contain information on all
-		 * contexts of a given PID.
+		 * between contexts. Only create for the first PID.
+		 * This is ok since same as debugfs, the log file will contain
+		 * information on all contexts of a given PID.
 		 */
 		binderfs_entry = binderfs_create_file(binder_binderfs_dir_entry_proc,
 			strbuf, &proc_fops, (void *)(unsigned long)proc->pid);
@@ -5281,10 +5284,8 @@ static int binder_open(struct inode *nodp, struct file *filp)
 			int error;
 
 			error = PTR_ERR(binderfs_entry);
-			if (error != -EEXIST) {
-				pr_warn("Unable to create file %s in binderfs (error %d)\n",
-					strbuf, error);
-			}
+			pr_warn("Unable to create file %s in binderfs (error %d)\n",
+				strbuf, error);
 		}
 	}
 
-- 
1.9.1