[PATCH] Take i_mutex in splice_from_pipe()
The splice_actor may be calling ->prepare_write() and ->commit_write(). We
want i_mutex on the inode being written to before calling those so that we
don't race i_size changes.
The double locking behavior is done elsewhere in splice.c, and if we
eventually want _nolock variants of generic_file_splice_write(), fs modules
might have to replicate the nasty locking code. We introduce
inode_double_lock() and inode_double_unlock() to consolidate the locking
rules into one set of functions.
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fs/splice.c b/fs/splice.c
index a567010..c1072b6 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -713,6 +713,7 @@
{
int ret, do_wakeup, err;
struct splice_desc sd;
+ struct inode *inode = out->f_mapping->host;
ret = 0;
do_wakeup = 0;
@@ -722,8 +723,13 @@
sd.file = out;
sd.pos = *ppos;
- if (pipe->inode)
- mutex_lock(&pipe->inode->i_mutex);
+ /*
+ * The actor worker might be calling ->prepare_write and
+ * ->commit_write. Most of the time, these expect i_mutex to
+ * be held. Since this may result in an ABBA deadlock with
+ * pipe->inode, we have to order lock acquiry here.
+ */
+ inode_double_lock(inode, pipe->inode);
for (;;) {
if (pipe->nrbufs) {
@@ -797,8 +803,7 @@
pipe_wait(pipe);
}
- if (pipe->inode)
- mutex_unlock(&pipe->inode->i_mutex);
+ inode_double_unlock(inode, pipe->inode);
if (do_wakeup) {
smp_mb();
@@ -1400,13 +1405,7 @@
* grabbing by inode address. Otherwise two different processes
* could deadlock (one doing tee from A -> B, the other from B -> A).
*/
- if (ipipe->inode < opipe->inode) {
- mutex_lock_nested(&ipipe->inode->i_mutex, I_MUTEX_PARENT);
- mutex_lock_nested(&opipe->inode->i_mutex, I_MUTEX_CHILD);
- } else {
- mutex_lock_nested(&opipe->inode->i_mutex, I_MUTEX_PARENT);
- mutex_lock_nested(&ipipe->inode->i_mutex, I_MUTEX_CHILD);
- }
+ inode_double_lock(ipipe->inode, opipe->inode);
do {
if (!opipe->readers) {
@@ -1450,8 +1449,7 @@
i++;
} while (len);
- mutex_unlock(&ipipe->inode->i_mutex);
- mutex_unlock(&opipe->inode->i_mutex);
+ inode_double_unlock(ipipe->inode, opipe->inode);
/*
* If we put data in the output pipe, wakeup any potential readers.