Re: [syzbot] [v9fs?] WARNING in v9fs_begin_writeback

[Edward Adam Davis]

debug

#syz test: upstream c0ecd6388360

diff --git a/fs/9p/fid.c b/fs/9p/fid.c
index de009a33e0e2..b5ccab74bb6f 100644
--- a/fs/9p/fid.c
+++ b/fs/9p/fid.c
@@ -13,6 +13,7 @@
 #include <linux/sched.h>
 #include <net/9p/9p.h>
 #include <net/9p/client.h>
+#include <linux/file.h>
 
 #include "v9fs.h"
 #include "v9fs_vfs.h"
diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index a97ceb105cd8..7768cc70439d 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -34,6 +34,7 @@ static void v9fs_begin_writeback(struct netfs_io_request *wreq)
 {
 	struct p9_fid *fid;
 
+	printk("ino: %lx, %s\n", wreq->inode->i_ino, __func__);
 	fid = v9fs_fid_find_inode(wreq->inode, true, INVALID_UID, true);
 	if (!fid) {
 		WARN_ONCE(1, "folio expected an open fid inode->i_ino=%lx\n",
diff --git a/fs/9p/vfs_dir.c b/fs/9p/vfs_dir.c
index e0d34e4e9076..3fe715ab6efd 100644
--- a/fs/9p/vfs_dir.c
+++ b/fs/9p/vfs_dir.c
@@ -219,6 +219,15 @@ int v9fs_dir_release(struct inode *inode, struct file *filp)
 			retval = filemap_fdatawrite(inode->i_mapping);
 
 		spin_lock(&inode->i_lock);
+		printk("del, ino: %lx, ino sync: %d, comm: %s, %s\n", inode->i_ino, inode->i_state & I_SYNC, current->comm, __func__);
+		if (I_SYNC & inode->i_state) {
+			spin_unlock(&inode->i_lock);
+			if (wait_on_bit_timeout(&inode->i_state, I_SYNC,
+						TASK_UNINTERRUPTIBLE, 5 * HZ))
+				return -EBUSY;
+			spin_lock(&inode->i_lock);
+		}
+
 		hlist_del(&fid->ilist);
 		spin_unlock(&inode->i_lock);
 		put_err = p9_fid_put(fid);
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 9258d30cffe3..4434bf37caa1 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -522,12 +522,23 @@ int netfs_writepages(struct address_space *mapping,
 	trace_netfs_write(wreq, netfs_write_trace_writeback);
 	netfs_stat(&netfs_n_wh_writepages);
 
+	unsigned long  i_state = wreq->inode->i_state;
+	wreq->inode->i_state |= I_SYNC;
+	printk("doing sync: %d, before sync: %d, ino: %lx, comm: %s, %s\n", wreq->inode->i_state & I_SYNC,
+			i_state & I_SYNC,
+			wreq->inode->i_ino, current->comm, __func__);
+	if (i_state & I_SYNC) {
+		error = -EBUSY;
+		goto couldnt_start;
+	}
+
 	do {
 		_debug("wbiter %lx %llx", folio->index, wreq->start + wreq->submitted);
 
 		/* It appears we don't have to handle cyclic writeback wrapping. */
 		WARN_ON_ONCE(wreq && folio_pos(folio) < wreq->start + wreq->submitted);
 
+		printk("ino: %lx, folio: %p, %s\n", wreq->inode->i_ino, folio, __func__);
 		if (netfs_folio_group(folio) != NETFS_FOLIO_COPY_TO_CACHE &&
 		    unlikely(!test_bit(NETFS_RREQ_UPLOAD_TO_SERVER, &wreq->flags))) {
 			set_bit(NETFS_RREQ_UPLOAD_TO_SERVER, &wreq->flags);
@@ -538,6 +549,9 @@ int netfs_writepages(struct address_space *mapping,
 		if (error < 0)
 			break;
 	} while ((folio = writeback_iter(mapping, wbc, folio, &error)));
+	wreq->inode->i_state &= ~I_SYNC;
+	printk("end sync: %d, ino: %lx, comm: %s, error: %d, %s\n", wreq->inode->i_state & I_SYNC,
+			wreq->inode->i_ino, current->comm, error, __func__);
 
 	for (int s = 0; s < NR_IO_STREAMS; s++)
 		netfs_issue_write(wreq, &wreq->io_streams[s]);