[v3] netfs, 9p: Fix race between umount and async request completion

Commit Message

David Howells May 24, 2024, 2:26 p.m. UTC

netfs, 9p: Fix race between umount and async request completion

There's a problem in 9p's interaction with netfslib whereby a crash occurs
because the 9p_fid structs get forcibly destroyed during client teardown
(without paying attention to their refcounts) before netfslib has finished
with them.  However, it's not a simple case of deferring the clunking that
p9_fid_put() does as that requires the p9_client record to still be
present.

The problem is that netfslib has to unlock pages and clear the IN_PROGRESS
flag before destroying the objects involved - including the fid - and, in
any case, nothing checks to see if writeback completed barring looking at
the page flags.

Fix this by keeping a count of outstanding I/O requests (of any type) and
waiting for it to quiesce during inode eviction.

Reported-by: [e-mail]
Link: https://lore.kernel.org/all/[e-mail]/
Reported-by: [e-mail]
Link: https://lore.kernel.org/all/[e-mail]/
Reported-by: [e-mail]
Link: https://lore.kernel.org/all/[e-mail]/
Signed-off-by: David Howells <[e-mail]>
Reviewed-by: Dominique Martinet <[e-mail]>
Tested-by: [e-mail]
cc: Eric Van Hensbergen <[e-mail]>
cc: Latchesar Ionkov <[e-mail]>
cc: Christian Schoenebeck <[e-mail]>
cc: Jeff Layton <[e-mail]>
cc: Steve French <[e-mail]>
cc: Hillf Danton <[e-mail]>
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
---
Notes:
    Changes
    =======
    ver #3)
     - Adjust commit message; no change to the diff.
    ver #2)
     - Wait for outstanding I/O before clobbering the pagecache.

 fs/9p/vfs_inode.c      |    1 +
 fs/afs/inode.c         |    1 +
 fs/netfs/objects.c     |    5 +++++
 fs/smb/client/cifsfs.c |    1 +
 include/linux/netfs.h  |   18 ++++++++++++++++++
 5 files changed, 26 insertions(+)

Comments

Christian Brauner May 27, 2024, 11:09 a.m. UTC | #1

On Fri, 24 May 2024 15:26:11 +0100, David Howells wrote:
> netfs, 9p: Fix race between umount and async request completion
> 
> There's a problem in 9p's interaction with netfslib whereby a crash occurs
> because the 9p_fid structs get forcibly destroyed during client teardown
> (without paying attention to their refcounts) before netfslib has finished
> with them.  However, it's not a simple case of deferring the clunking that
> p9_fid_put() does as that requires the p9_client record to still be
> present.
> 
> [...]

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] netfs, 9p: Fix race between umount and async request completion
      https://git.kernel.org/vfs/vfs/c/e20fe12bfb0b

Patch

diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index 8c9a896d691e..effb3aa1f3ed 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -349,6 +349,7 @@  void v9fs_evict_inode(struct inode *inode)
 	__le32 __maybe_unused version;
 
 	if (!is_bad_inode(inode)) {
+		netfs_wait_for_outstanding_io(inode);
 		truncate_inode_pages_final(&inode->i_data);
 
 		version = cpu_to_le32(v9inode->qid.version);
diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index 94fc049aff58..15bb7989c387 100644
--- a/fs/afs/inode.c
+++ b/fs/afs/inode.c
@@ -648,6 +648,7 @@  void afs_evict_inode(struct inode *inode)
 
 	ASSERTCMP(inode->i_ino, ==, vnode->fid.vnode);
 
+	netfs_wait_for_outstanding_io(inode);
 	truncate_inode_pages_final(&inode->i_data);
 
 	afs_set_cache_aux(vnode, &aux);
diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
index c90d482b1650..f4a642727479 100644
--- a/fs/netfs/objects.c
+++ b/fs/netfs/objects.c
@@ -72,6 +72,7 @@  struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 		}
 	}
 
+	atomic_inc(&ctx->io_count);
 	trace_netfs_rreq_ref(rreq->debug_id, 1, netfs_rreq_trace_new);
 	netfs_proc_add_rreq(rreq);
 	netfs_stat(&netfs_n_rh_rreq);
@@ -124,6 +125,7 @@  static void netfs_free_request(struct work_struct *work)
 {
 	struct netfs_io_request *rreq =
 		container_of(work, struct netfs_io_request, work);
+	struct netfs_inode *ictx = netfs_inode(rreq->inode);
 	unsigned int i;
 
 	trace_netfs_rreq(rreq, netfs_rreq_trace_free);
@@ -142,6 +144,9 @@  static void netfs_free_request(struct work_struct *work)
 		}
 		kvfree(rreq->direct_bv);
 	}
+
+	if (atomic_dec_and_test(&ictx->io_count))
+		wake_up_var(&ictx->io_count);
 	call_rcu(&rreq->rcu, netfs_free_request_rcu);
 }
 
diff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c
index ec5b639f421a..14810ffd15c8 100644
--- a/fs/smb/client/cifsfs.c
+++ b/fs/smb/client/cifsfs.c
@@ -431,6 +431,7 @@  cifs_free_inode(struct inode *inode)
 static void
 cifs_evict_inode(struct inode *inode)
 {
+	netfs_wait_for_outstanding_io(inode);
 	truncate_inode_pages_final(&inode->i_data);
 	if (inode->i_state & I_PINNING_NETFS_WB)
 		cifs_fscache_unuse_inode_cookie(inode, true);
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index d2d291a9cdad..3ca3906bb8da 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -68,6 +68,7 @@  struct netfs_inode {
 	loff_t			remote_i_size;	/* Size of the remote file */
 	loff_t			zero_point;	/* Size after which we assume there's no data
 						 * on the server */
+	atomic_t		io_count;	/* Number of outstanding reqs */
 	unsigned long		flags;
 #define NETFS_ICTX_ODIRECT	0		/* The file has DIO in progress */
 #define NETFS_ICTX_UNBUFFERED	1		/* I/O should not use the pagecache */
@@ -474,6 +475,7 @@  static inline void netfs_inode_init(struct netfs_inode *ctx,
 	ctx->remote_i_size = i_size_read(&ctx->inode);
 	ctx->zero_point = LLONG_MAX;
 	ctx->flags = 0;
+	atomic_set(&ctx->io_count, 0);
 #if IS_ENABLED(CONFIG_FSCACHE)
 	ctx->cache = NULL;
 #endif
@@ -517,4 +519,20 @@  static inline struct fscache_cookie *netfs_i_cookie(struct netfs_inode *ctx)
 #endif
 }
 
+/**
+ * netfs_wait_for_outstanding_io - Wait for outstanding I/O to complete
+ * @ctx: The netfs inode to wait on
+ *
+ * Wait for outstanding I/O requests of any type to complete.  This is intended
+ * to be called from inode eviction routines.  This makes sure that any
+ * resources held by those requests are cleaned up before we let the inode get
+ * cleaned up.
+ */
+static inline void netfs_wait_for_outstanding_io(struct inode *inode)
+{
+	struct netfs_inode *ictx = netfs_inode(inode);
+
+	wait_var_event(&ictx->io_count, atomic_read(&ictx->io_count) == 0);
+}
+
 #endif /* _LINUX_NETFS_H */