[PATCH v4 03/33] netfs: Fix a few minor bugs in netfs_page_mkwrite()

David Howells
2024-11-08T17:33:14Z

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

We can't return with VM_FAULT_SIGBUS | VM_FAULT_LOCKED; the core
code will not unlock the folio in this instance. Introduce a new
"unlock" error exit to handle this case. Use it to handle
the "folio is truncated" check, and change the "writeback interrupted
by a fatal signal" to do a NOPAGE exit instead of letting the core
code install the folio currently under writeback before killing the
process.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20241005182307.3190401-3-willy@infradead.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
fs/netfs/buffered_write.c | 27 +++++++++++++--------------
1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
index b3910dfcb56d..ff2814da88b1 100644
--- a/fs/netfs/buffered_write.c
+++ b/fs/netfs/buffered_write.c
@@ -491,7 +491,9 @@ EXPORT_SYMBOL(netfs_file_write_iter);

/*
* Notification that a previously read-only page is about to become writable.
- * Note that the caller indicates a single page of a multipage folio.
+ * The caller indicates the precise page that needs to be written to, but
+ * we only track group on a per-folio basis, so we block more often than
+ * we might otherwise.
*/
vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_group)
{
@@ -501,7 +503,7 @@ vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_gr
struct address_space *mapping = file->f_mapping;
struct inode *inode = file_inode(file);
struct netfs_inode *ictx = netfs_inode(inode);
- vm_fault_t ret = VM_FAULT_RETRY;
+ vm_fault_t ret = VM_FAULT_NOPAGE;
int err;

_enter("%lx", folio->index);
@@ -510,21 +512,15 @@ vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_gr

if (folio_lock_killable(folio) < 0)
goto out;
- if (folio->mapping != mapping) {
- folio_unlock(folio);
- ret = VM_FAULT_NOPAGE;
- goto out;
- }
-
- if (folio_wait_writeback_killable(folio)) {
- ret = VM_FAULT_LOCKED;
- goto out;
- }
+ if (folio->mapping != mapping)
+ goto unlock;
+ if (folio_wait_writeback_killable(folio) < 0)
+ goto unlock;

/* Can we see a streaming write here? */
if (WARN_ON(!folio_test_uptodate(folio))) {
- ret = VM_FAULT_SIGBUS | VM_FAULT_LOCKED;
- goto out;
+ ret = VM_FAULT_SIGBUS;
+ goto unlock;
}

group = netfs_folio_group(folio);
@@ -559,5 +555,8 @@ vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_gr
out:
sb_end_pagefault(inode->i_sb);
return ret;
+unlock:
+ folio_unlock(folio);
+ goto out;
}
EXPORT_SYMBOL(netfs_page_mkwrite);