fuse: allow parallel dio writes with FUSE_DIRECT_IO_ALLOW_MMAP

Instead of denying caching mode on parallel dio open, deny caching
open only while parallel dio are in-progress and wait for in-progress
parallel dio writes before entering inode caching io mode.

This allows executing parallel dio when inode is not in caching mode
even if shared mmap is allowed, but no mmaps have been performed on
the inode in question.

An mmap on direct_io file now waits for all in-progress parallel dio
writes to complete, so parallel dio writes together with
FUSE_DIRECT_IO_ALLOW_MMAP is enabled by this commit.

Signed-off-by: Bernd Schubert <bschubert@ddn.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 29 insertions, 12 deletions

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 9af356fbc578..0a551a147673 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1335,6 +1335,7 @@ static bool fuse_dio_wr_exclusive_lock(struct kiocb *iocb, struct iov_iter *from
 	struct file *file = iocb->ki_filp;
 	struct fuse_file *ff = file->private_data;
 	struct inode *inode = file_inode(iocb->ki_filp);
+	struct fuse_inode *fi = get_fuse_inode(inode);
 
 	/* Server side has to advise that it supports parallel dio writes. */
 	if (!(ff->open_flags & FOPEN_PARALLEL_DIRECT_WRITES))
@@ -1347,12 +1348,9 @@ static bool fuse_dio_wr_exclusive_lock(struct kiocb *iocb, struct iov_iter *from
 	if (iocb->ki_flags & IOCB_APPEND)
 		return true;
 
-	/*
-	 * Combination of page access and direct-io is difficult, shared locks
-	 * actually introduce a conflict.
-	 */
-	if (get_fuse_conn(inode)->direct_io_allow_mmap)
-		return true;
+	/* shared locks are not allowed with parallel page cache IO */
+	if (test_bit(FUSE_I_CACHE_IO_MODE, &fi->state))
+		return false;
 
 	/* Parallel dio beyond EOF is not supported, at least for now. */
 	if (fuse_io_past_eof(iocb, from))
@@ -1365,6 +1363,7 @@ static void fuse_dio_lock(struct kiocb *iocb, struct iov_iter *from,
 			  bool *exclusive)
 {
 	struct inode *inode = file_inode(iocb->ki_filp);
+	struct fuse_file *ff = iocb->ki_filp->private_data;
 
 	*exclusive = fuse_dio_wr_exclusive_lock(iocb, from);
 	if (*exclusive) {
@@ -1372,10 +1371,14 @@ static void fuse_dio_lock(struct kiocb *iocb, struct iov_iter *from,
 	} else {
 		inode_lock_shared(inode);
 		/*
-		 * Previous check was without inode lock and might have raced,
-		 * check again.
+		 * New parallal dio allowed only if inode is not in caching
+		 * mode and denies new opens in caching mode. This check
+		 * should be performed only after taking shared inode lock.
+		 * Previous past eof check was without inode lock and might
+		 * have raced, so check it again.
 		 */
-		if (fuse_io_past_eof(iocb, from)) {
+		if (fuse_io_past_eof(iocb, from) ||
+		    fuse_file_uncached_io_start(inode, ff) != 0) {
 			inode_unlock_shared(inode);
 			inode_lock(inode);
 			*exclusive = true;
@@ -1383,11 +1386,16 @@ static void fuse_dio_lock(struct kiocb *iocb, struct iov_iter *from,
 	}
 }
 
-static void fuse_dio_unlock(struct inode *inode, bool exclusive)
+static void fuse_dio_unlock(struct kiocb *iocb, bool exclusive)
 {
+	struct inode *inode = file_inode(iocb->ki_filp);
+	struct fuse_file *ff = iocb->ki_filp->private_data;
+
 	if (exclusive) {
 		inode_unlock(inode);
 	} else {
+		/* Allow opens in caching mode after last parallel dio end */
+		fuse_file_uncached_io_end(inode, ff);
 		inode_unlock_shared(inode);
 	}
 }
@@ -1669,7 +1677,7 @@ static ssize_t fuse_direct_write_iter(struct kiocb *iocb, struct iov_iter *from)
 			fuse_write_update_attr(inode, iocb->ki_pos, res);
 		}
 	}
-	fuse_dio_unlock(inode, exclusive);
+	fuse_dio_unlock(iocb, exclusive);
 
 	return res;
 }
@@ -2523,6 +2531,10 @@ static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma)
 	if (FUSE_IS_DAX(file_inode(file)))
 		return fuse_dax_mmap(file, vma);
 
+	/*
+	 * FOPEN_DIRECT_IO handling is special compared to O_DIRECT,
+	 * as does not allow MAP_SHARED mmap without FUSE_DIRECT_IO_ALLOW_MMAP.
+	 */
 	if (ff->open_flags & FOPEN_DIRECT_IO) {
 		/*
 		 * Can't provide the coherency needed for MAP_SHARED
@@ -2538,7 +2550,11 @@ static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma)
 			return generic_file_mmap(file, vma);
 		}
 
-		/* First mmap of direct_io file enters caching inode io mode. */
+		/*
+		 * First mmap of direct_io file enters caching inode io mode.
+		 * Also waits for parallel dio writers to go into serial mode
+		 * (exclusive instead of shared lock).
+		 */
 		rc = fuse_file_cached_io_start(file_inode(file), ff);
 		if (rc)
 			return rc;
@@ -3312,6 +3328,7 @@ void fuse_init_file_inode(struct inode *inode, unsigned int flags)
 	fi->writectr = 0;
 	fi->iocachectr = 0;
 	init_waitqueue_head(&fi->page_waitq);
+	init_waitqueue_head(&fi->direct_io_waitq);
 	fi->writepages = RB_ROOT;
 
 	if (IS_ENABLED(CONFIG_FUSE_DAX))