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fuse: fix parallel dio write on file open in passthrough mode 

Parallel dio write takes a negative refcount of fi->iocachectr and so does
open of file in passthrough mode.

The refcount of passthrough mode is associated with attach/detach of a
fuse_backing object to fuse inode.

For parallel dio write, the backing file is irrelevant, so the call to
fuse_inode_uncached_io_start() passes a NULL fuse_backing object.

Passing a NULL fuse_backing will result in false -EBUSY error if the file
is already open in passthrough mode.

Allow taking negative fi->iocachectr refcount with NULL fuse_backing,
because it does not conflict with an already attached fuse_backing object.

Fixes: 4a90451bbc ("fuse: implement open in passthrough mode")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Amir Goldstein 2024-04-07 18:57:57 +03:00 committed by Miklos Szeredi
parent 4864a6dd83
commit 7cc9112628
1 changed files with 2 additions and 2 deletions
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4
fs/fuse/iomode.c
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@ -90,7 +90,7 @@ int fuse_inode_uncached_io_start(struct fuse_inode *fi, struct fuse_backing *fb)
spin_lock(&fi->lock);
/* deny conflicting backing files on same fuse inode */
oldfb = fuse_inode_backing(fi);
if (oldfb && oldfb != fb) {
if (fb && oldfb && oldfb != fb) {
err = -EBUSY;
goto unlock;
}
@ -101,7 +101,7 @@ int fuse_inode_uncached_io_start(struct fuse_inode *fi, struct fuse_backing *fb)
fi->iocachectr--;
/* fuse inode holds a single refcount of backing file */
if (!oldfb) {
if (fb && !oldfb) {
oldfb = fuse_inode_backing_set(fi, fb);
WARN_ON_ONCE(oldfb != NULL);
} else {