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Date: Tue, 2 Dec 2014 13:24:19 -0500
From: Jeff Layton <jlayton@...marydata.com>
To: linux-nfs@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
Al Viro <viro@...iv.linux.org.uk>
Subject: [RFC PATCH 10/14] nfsd: keep a reference to the fs_struct in svc_rqst
When we convert this code to use a workqueue, we won't want to allocate
a new fs_struct to handle each RPC. Doing so might also be problematic
since we'd be swapping out the ->fs value on a "public" workqueue
kthread.
Change the code to allocate an fs struct when when allocating a svc_rqst
and then switch to using that in the "nfsd" function.
Cc: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Jeff Layton <jlayton@...marydata.com>
---
fs/fs_struct.c | 59 +++++++++++++++++++++++++++++++++++++++-------
fs/nfsd/nfssvc.c | 17 ++++++-------
include/linux/fs_struct.h | 3 +++
include/linux/sunrpc/svc.h | 1 +
net/sunrpc/svc.c | 8 +++++++
5 files changed, 69 insertions(+), 19 deletions(-)
diff --git a/fs/fs_struct.c b/fs/fs_struct.c
index 7dca743b2ce1..9bc08ea2f433 100644
--- a/fs/fs_struct.c
+++ b/fs/fs_struct.c
@@ -127,26 +127,67 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old)
}
return fs;
}
+EXPORT_SYMBOL_GPL(copy_fs_struct);
-int unshare_fs_struct(void)
+/* Replace current fs struct with one given. Return a pointer to old one. */
+static struct fs_struct *
+swap_fs_struct(struct fs_struct *new_fs)
{
- struct fs_struct *fs = current->fs;
- struct fs_struct *new_fs = copy_fs_struct(fs);
- int kill;
-
- if (!new_fs)
- return -ENOMEM;
+ struct fs_struct *old_fs;
task_lock(current);
+ old_fs = current->fs;
+ current->fs = new_fs;
+ task_unlock(current);
+
+ return old_fs;
+}
+
+/* Put a reference to a fs_struct. */
+void put_fs_struct(struct fs_struct *fs)
+{
+ bool kill;
+
spin_lock(&fs->lock);
kill = !--fs->users;
- current->fs = new_fs;
spin_unlock(&fs->lock);
- task_unlock(current);
if (kill)
free_fs_struct(fs);
+}
+EXPORT_SYMBOL_GPL(put_fs_struct);
+
+/* Take an extra reference to a fs_struct. Caller must already hold one! */
+struct fs_struct *
+get_fs_struct(struct fs_struct *fs)
+{
+ spin_lock(&fs->lock);
+ ++fs->users;
+ spin_unlock(&fs->lock);
+ return fs;
+}
+EXPORT_SYMBOL_GPL(get_fs_struct);
+
+/*
+ * Swap in a new fs_struct and drop the reference on the old one.
+ * Caller must have already taken the reference to the new one.
+ */
+void replace_fs_struct(struct fs_struct *new_fs)
+{
+ struct fs_struct *old_fs = swap_fs_struct(new_fs);
+
+ put_fs_struct(old_fs);
+}
+EXPORT_SYMBOL_GPL(replace_fs_struct);
+
+int unshare_fs_struct(void)
+{
+ struct fs_struct *new_fs = copy_fs_struct(current->fs);
+
+ if (!new_fs)
+ return -ENOMEM;
+ replace_fs_struct(new_fs);
return 0;
}
EXPORT_SYMBOL_GPL(unshare_fs_struct);
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index 71e7b180c0d9..f37bd7db2176 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -582,15 +582,13 @@ nfsd(void *vrqstp)
/* Lock module and set up kernel thread */
mutex_lock(&nfsd_mutex);
- /* At this point, the thread shares current->fs
- * with the init process. We need to create files with a
- * umask of 0 instead of init's umask. */
- if (unshare_fs_struct() < 0) {
- printk("Unable to start nfsd thread: out of memory\n");
- goto out;
- }
-
- current->fs->umask = 0;
+ /*
+ * At this point, the thread shares current->fs with the init process.
+ * We need to create files with a umask of 0 instead of init's umask,
+ * so switch to the fs_struct associated with the rqstp.
+ */
+ get_fs_struct(rqstp->rq_fs);
+ replace_fs_struct(rqstp->rq_fs);
/*
* thread is spawned with all signals set to SIG_IGN, re-enable
@@ -632,7 +630,6 @@ nfsd(void *vrqstp)
mutex_lock(&nfsd_mutex);
nfsdstats.th_cnt --;
-out:
rqstp->rq_server = NULL;
/* Release the thread */
diff --git a/include/linux/fs_struct.h b/include/linux/fs_struct.h
index 0efc3e62843a..d2b7a1942790 100644
--- a/include/linux/fs_struct.h
+++ b/include/linux/fs_struct.h
@@ -21,7 +21,10 @@ extern void set_fs_root(struct fs_struct *, const struct path *);
extern void set_fs_pwd(struct fs_struct *, const struct path *);
extern struct fs_struct *copy_fs_struct(struct fs_struct *);
extern void free_fs_struct(struct fs_struct *);
+extern void replace_fs_struct(struct fs_struct *);
extern int unshare_fs_struct(void);
+struct fs_struct *get_fs_struct(struct fs_struct *);
+void put_fs_struct(struct fs_struct *);
static inline void get_fs_root(struct fs_struct *fs, struct path *root)
{
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 81e723220346..f47de87660b4 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -295,6 +295,7 @@ struct svc_rqst {
struct svc_cacherep * rq_cacherep; /* cache info */
struct task_struct *rq_task; /* service thread */
spinlock_t rq_lock; /* per-request lock */
+ struct fs_struct *rq_fs;
};
#define SVC_NET(svc_rqst) (svc_rqst->rq_xprt->xpt_net)
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 7c8e33923210..4300bc852f6e 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -20,6 +20,7 @@
#include <linux/module.h>
#include <linux/kthread.h>
#include <linux/slab.h>
+#include <linux/fs_struct.h>
#include <linux/sunrpc/types.h>
#include <linux/sunrpc/xdr.h>
@@ -622,6 +623,11 @@ svc_rqst_alloc(struct svc_serv *serv, struct svc_pool *pool, int node)
if (!svc_init_buffer(rqstp, serv->sv_max_mesg, node))
goto out_enomem;
+ rqstp->rq_fs = copy_fs_struct(current->fs);
+ if (!rqstp->rq_fs)
+ goto out_enomem;
+
+ rqstp->rq_fs->umask = 0;
return rqstp;
out_enomem:
svc_rqst_free(rqstp);
@@ -784,6 +790,8 @@ svc_rqst_free(struct svc_rqst *rqstp)
kfree(rqstp->rq_resp);
kfree(rqstp->rq_argp);
kfree(rqstp->rq_auth_data);
+ if (rqstp->rq_fs)
+ put_fs_struct(rqstp->rq_fs);
kfree_rcu(rqstp, rq_rcu_head);
}
EXPORT_SYMBOL_GPL(svc_rqst_free);
--
2.1.0
--
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