[ 097/108] eCryptfs: Fix lockdep warning in miscdev operations

Ben Hutchings
2012-07-23T01:42:42Z

From: Tyler Hicks <tyhicks@canonical.com>

commit 60d65f1f07a7d81d3eb3b91fc13fca80f2fdbb12 upstream.

Don't grab the daemon mutex while holding the message context mutex.
Addresses this lockdep warning:

ecryptfsd/2141 is trying to acquire lock:
(&ecryptfs_msg_ctx_arr[i].mux){+.+.+.}, at: [<ffffffffa029c213>] ecryptfs_miscdev_read+0x143/0x470 [ecryptfs]

but task is already holding lock:
(&(*daemon)->mux){+.+...}, at: [<ffffffffa029c2ec>] ecryptfs_miscdev_read+0x21c/0x470 [ecryptfs]

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&(*daemon)->mux){+.+...}:
[<ffffffff810a3b8d>] lock_acquire+0x9d/0x220
[<ffffffff8151c6da>] __mutex_lock_common+0x5a/0x4b0
[<ffffffff8151cc64>] mutex_lock_nested+0x44/0x50
[<ffffffffa029c5d7>] ecryptfs_send_miscdev+0x97/0x120 [ecryptfs]
[<ffffffffa029b744>] ecryptfs_send_message+0x134/0x1e0 [ecryptfs]
[<ffffffffa029a24e>] ecryptfs_generate_key_packet_set+0x2fe/0xa80 [ecryptfs]
[<ffffffffa02960f8>] ecryptfs_write_metadata+0x108/0x250 [ecryptfs]
[<ffffffffa0290f80>] ecryptfs_create+0x130/0x250 [ecryptfs]
[<ffffffff811963a4>] vfs_create+0xb4/0x120
[<ffffffff81197865>] do_last+0x8c5/0xa10
[<ffffffff811998f9>] path_openat+0xd9/0x460
[<ffffffff81199da2>] do_filp_open+0x42/0xa0
[<ffffffff81187998>] do_sys_open+0xf8/0x1d0
[<ffffffff81187a91>] sys_open+0x21/0x30
[<ffffffff81527d69>] system_call_fastpath+0x16/0x1b

-> #0 (&ecryptfs_msg_ctx_arr[i].mux){+.+.+.}:
[<ffffffff810a3418>] __lock_acquire+0x1bf8/0x1c50
[<ffffffff810a3b8d>] lock_acquire+0x9d/0x220
[<ffffffff8151c6da>] __mutex_lock_common+0x5a/0x4b0
[<ffffffff8151cc64>] mutex_lock_nested+0x44/0x50
[<ffffffffa029c213>] ecryptfs_miscdev_read+0x143/0x470 [ecryptfs]
[<ffffffff811887d3>] vfs_read+0xb3/0x180
[<ffffffff811888ed>] sys_read+0x4d/0x90
[<ffffffff81527d69>] system_call_fastpath+0x16/0x1b

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/ecryptfs/miscdev.c | 25 +++++++++++++------------
1 file changed, 13 insertions(+), 12 deletions(-)

--- a/fs/ecryptfs/miscdev.c
+++ b/fs/ecryptfs/miscdev.c
@@ -195,31 +195,32 @@ int ecryptfs_send_miscdev(char *data, si
struct ecryptfs_msg_ctx *msg_ctx, u8 msg_type,
u16 msg_flags, struct ecryptfs_daemon *daemon)
{
- int rc = 0;
+ struct ecryptfs_message *msg;

- mutex_lock(&msg_ctx->mux);
- msg_ctx->msg = kmalloc((sizeof(*msg_ctx->msg) + data_size),
- GFP_KERNEL);
- if (!msg_ctx->msg) {
- rc = -ENOMEM;
+ msg = kmalloc((sizeof(*msg) + data_size), GFP_KERNEL);
+ if (!msg) {
printk(KERN_ERR "%s: Out of memory whilst attempting "
"to kmalloc(%zd, GFP_KERNEL)\n", __func__,
- (sizeof(*msg_ctx->msg) + data_size));
- goto out_unlock;
+ (sizeof(*msg) + data_size));
+ return -ENOMEM;
}
+
+ mutex_lock(&msg_ctx->mux);
+ msg_ctx->msg = msg;
msg_ctx->msg->index = msg_ctx->index;
msg_ctx->msg->data_len = data_size;
msg_ctx->type = msg_type;
memcpy(msg_ctx->msg->data, data, data_size);
msg_ctx->msg_size = (sizeof(*msg_ctx->msg) + data_size);
- mutex_lock(&daemon->mux);
list_add_tail(&msg_ctx->daemon_out_list, &daemon->msg_ctx_out_queue);
+ mutex_unlock(&msg_ctx->mux);
+
+ mutex_lock(&daemon->mux);
daemon->num_queued_msg_ctx++;
wake_up_interruptible(&daemon->wait);
mutex_unlock(&daemon->mux);
-out_unlock:
- mutex_unlock(&msg_ctx->mux);
- return rc;
+
+ return 0;
}

/**