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authorMark Fasheh <mark.fasheh@oracle.com>2006-10-17 10:31:38 +0200
committerJens Axboe <axboe@nelson.home.kernel.dk>2006-10-19 20:53:08 +0200
commit62752ee198dca9209b7dee504763e51b11e9e0ca (patch)
tree5e340a4c690851dadc3a8aa395e4c0d14b4837eb
parentce9e3d9953c8cb67001719b5516da2928e956be4 (diff)
downloadop-kernel-dev-62752ee198dca9209b7dee504763e51b11e9e0ca.zip
op-kernel-dev-62752ee198dca9209b7dee504763e51b11e9e0ca.tar.gz
[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>
-rw-r--r--fs/inode.c36
-rw-r--r--fs/splice.c24
-rw-r--r--include/linux/fs.h3
3 files changed, 50 insertions, 13 deletions
diff --git a/fs/inode.c b/fs/inode.c
index d9a21d1..26cdb11 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1306,6 +1306,42 @@ void wake_up_inode(struct inode *inode)
wake_up_bit(&inode->i_state, __I_LOCK);
}
+/*
+ * We rarely want to lock two inodes that do not have a parent/child
+ * relationship (such as directory, child inode) simultaneously. The
+ * vast majority of file systems should be able to get along fine
+ * without this. Do not use these functions except as a last resort.
+ */
+void inode_double_lock(struct inode *inode1, struct inode *inode2)
+{
+ if (inode1 == NULL || inode2 == NULL || inode1 == inode2) {
+ if (inode1)
+ mutex_lock(&inode1->i_mutex);
+ else if (inode2)
+ mutex_lock(&inode2->i_mutex);
+ return;
+ }
+
+ if (inode1 < inode2) {
+ mutex_lock_nested(&inode1->i_mutex, I_MUTEX_PARENT);
+ mutex_lock_nested(&inode2->i_mutex, I_MUTEX_CHILD);
+ } else {
+ mutex_lock_nested(&inode2->i_mutex, I_MUTEX_PARENT);
+ mutex_lock_nested(&inode1->i_mutex, I_MUTEX_CHILD);
+ }
+}
+EXPORT_SYMBOL(inode_double_lock);
+
+void inode_double_unlock(struct inode *inode1, struct inode *inode2)
+{
+ if (inode1)
+ mutex_unlock(&inode1->i_mutex);
+
+ if (inode2 && inode2 != inode1)
+ mutex_unlock(&inode2->i_mutex);
+}
+EXPORT_SYMBOL(inode_double_unlock);
+
static __initdata unsigned long ihash_entries;
static int __init set_ihash_entries(char *str)
{
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 @@ ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
{
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 @@ ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
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 @@ ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
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 @@ static int link_pipe(struct pipe_inode_info *ipipe,
* 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 @@ static int link_pipe(struct pipe_inode_info *ipipe,
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.
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 661c7c5..853a02f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -623,6 +623,9 @@ enum inode_i_mutex_lock_class
I_MUTEX_QUOTA
};
+extern void inode_double_lock(struct inode *inode1, struct inode *inode2);
+extern void inode_double_unlock(struct inode *inode1, struct inode *inode2);
+
/*
* NOTE: in a 32bit arch with a preemptable kernel and
* an UP compile the i_size_read/write must be atomic
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