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Message-ID: <20150608055731.GD21465@mtj.duckdns.org>
Date: Mon, 8 Jun 2015 14:57:31 +0900
From: Tejun Heo <tj@...nel.org>
To: Sasha Levin <sasha.levin@...cle.com>,
Eric Van Hensbergen <ericvh@...il.com>,
Ron Minnich <rminnich@...dia.gov>,
Latchesar Ionkov <lucho@...kov.net>,
v9fs-developer@...ts.sourceforge.net
Cc: axboe@...nel.dk, linux-kernel@...r.kernel.org, jack@...e.cz,
hch@...radead.org, hannes@...xchg.org,
linux-fsdevel@...r.kernel.org, vgoyal@...hat.com,
lizefan@...wei.com, cgroups@...r.kernel.org, linux-mm@...ck.org,
mhocko@...e.cz, clm@...com, fengguang.wu@...el.com,
david@...morbit.com, gthelen@...gle.com, khlebnikov@...dex-team.ru
Subject: [PATCH block/for-4.2-writeback] v9fs: fix error handling in
v9fs_session_init()
On failure, v9fs_session_init() returns with the v9fs_session_info
struct partially initialized and expects the caller to invoke
v9fs_session_close() to clean it up; however, it doesn't track whether
the bdi is initialized or not and curiously invokes bdi_destroy() in
both vfs_session_init() failure path too.
A. If v9fs_session_init() fails before the bdi is initialized, the
follow-up v9fs_session_close() will invoke bdi_destroy() on an
uninitialized bdi.
B. If v9fs_session_init() fails after the bdi is initialized,
bdi_destroy() will be called twice on the same bdi - once in the
failure path of v9fs_session_init() and then by
v9fs_session_close().
A is broken no matter what. B used to be okay because bdi_destroy()
allowed being invoked multiple times on the same bdi, which BTW was
broken in its own way - if bdi_destroy() was invoked on an initialiezd
but !registered bdi, it'd fail to free percpu counters. Since
f0054bb1e1f3 ("writeback: move backing_dev_info->wb_lock and
->worklist into bdi_writeback"), this no longer work - bdi_destroy()
on an initialized but not registered bdi works correctly but multiple
invocations of bdi_destroy() is no longer allowed.
The obvious culprit here is v9fs_session_init()'s odd and broken error
behavior. It should simply clean up after itself on failures. This
patch makes the following updates to v9fs_session_init().
* @rc -> @retval error return propagation removed. It didn't serve
any purpose. Just use @rc.
* Move addition to v9fs_sessionlist to the end of the function so that
incomplete sessions are not put on the list or iterated and error
path doesn't have to worry about it.
* Update error handling so that it cleans up after itself.
Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Sasha Levin <sasha.levin@...cle.com>
---
fs/9p/v9fs.c | 50 ++++++++++++++++++++++----------------------------
fs/9p/vfs_super.c | 8 ++------
2 files changed, 24 insertions(+), 34 deletions(-)
diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 620d934..8aa56bb 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -320,31 +320,21 @@ static int v9fs_parse_options(struct v9fs_session_info *v9ses, char *opts)
struct p9_fid *v9fs_session_init(struct v9fs_session_info *v9ses,
const char *dev_name, char *data)
{
- int retval = -EINVAL;
struct p9_fid *fid;
- int rc;
+ int rc = -ENOMEM;
v9ses->uname = kstrdup(V9FS_DEFUSER, GFP_KERNEL);
if (!v9ses->uname)
- return ERR_PTR(-ENOMEM);
+ goto err_names;
v9ses->aname = kstrdup(V9FS_DEFANAME, GFP_KERNEL);
- if (!v9ses->aname) {
- kfree(v9ses->uname);
- return ERR_PTR(-ENOMEM);
- }
+ if (!v9ses->aname)
+ goto err_names;
init_rwsem(&v9ses->rename_sem);
rc = bdi_setup_and_register(&v9ses->bdi, "9p");
- if (rc) {
- kfree(v9ses->aname);
- kfree(v9ses->uname);
- return ERR_PTR(rc);
- }
-
- spin_lock(&v9fs_sessionlist_lock);
- list_add(&v9ses->slist, &v9fs_sessionlist);
- spin_unlock(&v9fs_sessionlist_lock);
+ if (rc)
+ goto err_names;
v9ses->uid = INVALID_UID;
v9ses->dfltuid = V9FS_DEFUID;
@@ -352,10 +342,9 @@ struct p9_fid *v9fs_session_init(struct v9fs_session_info *v9ses,
v9ses->clnt = p9_client_create(dev_name, data);
if (IS_ERR(v9ses->clnt)) {
- retval = PTR_ERR(v9ses->clnt);
- v9ses->clnt = NULL;
+ rc = PTR_ERR(v9ses->clnt);
p9_debug(P9_DEBUG_ERROR, "problem initializing 9p client\n");
- goto error;
+ goto err_bdi;
}
v9ses->flags = V9FS_ACCESS_USER;
@@ -368,10 +357,8 @@ struct p9_fid *v9fs_session_init(struct v9fs_session_info *v9ses,
}
rc = v9fs_parse_options(v9ses, data);
- if (rc < 0) {
- retval = rc;
- goto error;
- }
+ if (rc < 0)
+ goto err_clnt;
v9ses->maxdata = v9ses->clnt->msize - P9_IOHDRSZ;
@@ -405,10 +392,9 @@ struct p9_fid *v9fs_session_init(struct v9fs_session_info *v9ses,
fid = p9_client_attach(v9ses->clnt, NULL, v9ses->uname, INVALID_UID,
v9ses->aname);
if (IS_ERR(fid)) {
- retval = PTR_ERR(fid);
- fid = NULL;
+ rc = PTR_ERR(fid);
p9_debug(P9_DEBUG_ERROR, "cannot attach\n");
- goto error;
+ goto err_clnt;
}
if ((v9ses->flags & V9FS_ACCESS_MASK) == V9FS_ACCESS_SINGLE)
@@ -420,12 +406,20 @@ struct p9_fid *v9fs_session_init(struct v9fs_session_info *v9ses,
/* register the session for caching */
v9fs_cache_session_get_cookie(v9ses);
#endif
+ spin_lock(&v9fs_sessionlist_lock);
+ list_add(&v9ses->slist, &v9fs_sessionlist);
+ spin_unlock(&v9fs_sessionlist_lock);
return fid;
-error:
+err_clnt:
+ p9_client_destroy(v9ses->clnt);
+err_bdi:
bdi_destroy(&v9ses->bdi);
- return ERR_PTR(retval);
+err_names:
+ kfree(v9ses->uname);
+ kfree(v9ses->aname);
+ return ERR_PTR(rc);
}
/**
diff --git a/fs/9p/vfs_super.c b/fs/9p/vfs_super.c
index e99a338..bf495ce 100644
--- a/fs/9p/vfs_super.c
+++ b/fs/9p/vfs_super.c
@@ -130,11 +130,7 @@ static struct dentry *v9fs_mount(struct file_system_type *fs_type, int flags,
fid = v9fs_session_init(v9ses, dev_name, data);
if (IS_ERR(fid)) {
retval = PTR_ERR(fid);
- /*
- * we need to call session_close to tear down some
- * of the data structure setup by session_init
- */
- goto close_session;
+ goto free_session;
}
sb = sget(fs_type, NULL, v9fs_set_super, flags, v9ses);
@@ -195,8 +191,8 @@ static struct dentry *v9fs_mount(struct file_system_type *fs_type, int flags,
clunk_fid:
p9_client_clunk(fid);
-close_session:
v9fs_session_close(v9ses);
+free_session:
kfree(v9ses);
return ERR_PTR(retval);
--
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