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smb: client: fix busy dentry warning on unmount after DIO

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Commit c68337442f ("cifs: Fix busy dentry used after unmounting") fixed
the issue in cifs where deferred close of a file led to a dentry reference
count not being released in umount, by flushing deferredclose_wq in
cifs_kill_sb() to solve it.

However, the cifs DIO path suffers from the same busy-dentry problem caused
by a delayed dentry reference-count release:

	[dio]			[cifsd]			[close + umount]
netfs_unbuffered_write_iter_locked
...
				cifs_demultiplex_thread
 netfs_unbuffered_write
  cifs_issue_write
  netfs_wait_for_in_progress_stream [1]
				...
				 netfs_write_subrequest_terminated
				  netfs_subreq_clear_in_progress
				   netfs_wake_collector // wake [1]
				  netfs_put_subrequest
 netfs_put_request
  queue_work(system_dfl_wq, xxx) [2]
 // dio write return					cifs_close
							 _cifsFileInfo_put
							  // cfile->count 2->1
							  --cfile->count [3]

							// umount
							cifs_kill_sb
							 kill_anon_super
							  // warning triggered!
							  shrink_dcache_for_umount [4]
[system_dfl_wq] [5]
netfs_free_request
 ...
 _cifsFileInfo_put
  // cfile->count 1->0
  --cfile->count
  queue_work(fileinfo_put_wq, xxx)

[fileinfo_put_wq] [6]
cifsFileInfo_put_work
 cifsFileInfo_put_final
  dput

If the umount path is triggered before [5], it results warning:
BUG: Dentry 00000000eab1f070{i=9a917b66ae404fec,n=test}  still in use (1)
[unmount of cifs cifs]

The existing per-inode ictx->io_count wait in cifs_evict_inode() does not
help: it lives in the inode eviction path, which runs after
shrink_dcache_for_umount() has already warned about the busy dentries.

Fix it by adding a per-superblock outstanding-rreq counter that is
incremented in cifs_init_request() and decremented in cifs_free_request().
In cifs_kill_sb(), before kill_anon_super(), wait for this counter to reach
0 - which guarantees that all cleanup_work for this sb have run and thus
all relevant cfile puts are queued on fileinfo_put_wq or serverclose_wq.
Then drain the workqueue so the dentry refs are dropped.

This is a targeted wait, not a flush of the system-wide system_dfl_wq.

Fixes: 340cea84f6 ("cifs: open files should not hold ref on superblock")
Signed-off-by: Zizhi Wo <wozizhi@huawei.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
This commit is contained in:
Zizhi Wo
2026-07-04 09:53:20 +08:00
committed by Steve French
parent 608362facd
commit 75f5c412fa
4 changed files with 19 additions and 0 deletions
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1
fs/smb/client/cifs_fs_sb.h
View File

@@ -56,6 +56,7 @@ struct cifs_sb_info {
struct smb3_fs_context *ctx;
atomic_t active;
atomic_t mnt_cifs_flags;
atomic_t outstanding_rreq; /* nr of rreqs not yet fully deinitialized */
struct delayed_work prune_tlinks;
struct rcu_head rcu;

12
fs/smb/client/cifsfs.c
View File

@@ -311,6 +311,18 @@ static void cifs_kill_sb(struct super_block *sb)
/* Wait for all opened files to release */
flush_workqueue(deferredclose_wq);
/*
* Wait for all in-flight netfs I/O requests to finish their
* cleanup_work so that any cifsFileInfo final puts they queue
* to fileinfo_put_wq/serverclose_wq have been queued, then
* drain the workqueue so the cfile dentry refs are dropped to
* avoid the busy dentry warning.
*/
wait_var_event(&cifs_sb->outstanding_rreq,
!atomic_read(&cifs_sb->outstanding_rreq));
flush_workqueue(serverclose_wq);
flush_workqueue(fileinfo_put_wq);
/* finally release root dentry */
dput(cifs_sb->root);
cifs_sb->root = NULL;

1
fs/smb/client/connect.c
View File

@@ -3485,6 +3485,7 @@ int cifs_setup_cifs_sb(struct cifs_sb_info *cifs_sb)
spin_lock_init(&cifs_sb->tlink_tree_lock);
cifs_sb->tlink_tree = RB_ROOT;
atomic_set(&cifs_sb->outstanding_rreq, 0);
cifs_dbg(FYI, "file mode: %04ho dir mode: %04ho\n",
ctx->file_mode, ctx->dir_mode);

5
fs/smb/client/file.c
View File

@@ -288,6 +288,7 @@ static int cifs_init_request(struct netfs_io_request *rreq, struct file *file)
return smb_EIO1(smb_eio_trace_not_netfs_writeback, rreq->origin);
}
atomic_inc(&cifs_sb->outstanding_rreq);
return 0;
}
@@ -309,9 +310,13 @@ static void cifs_rreq_done(struct netfs_io_request *rreq)
static void cifs_free_request(struct netfs_io_request *rreq)
{
struct cifs_io_request *req = container_of(rreq, struct cifs_io_request, rreq);
struct cifs_sb_info *cifs_sb = CIFS_SB(rreq->inode->i_sb);
if (req->cfile)
cifsFileInfo_put(req->cfile);
if (atomic_dec_and_test(&cifs_sb->outstanding_rreq))
wake_up_var(&cifs_sb->outstanding_rreq);
}
static void cifs_free_subrequest(struct netfs_io_subrequest *subreq)