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NFS: Fix a race when updating an existing write

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commit 76d2e3890fb169168c73f2e4f8375c7cc24a765e upstream.

After nfs_lock_and_join_requests() tests for whether the request is
still attached to the mapping, nothing prevents a call to
nfs_inode_remove_request() from succeeding until we actually lock the
page group.
The reason is that whoever called nfs_inode_remove_request() doesn't
necessarily have a lock on the page group head.

So in order to avoid races, let's take the page group lock earlier in
nfs_lock_and_join_requests(), and hold it across the removal of the
request in nfs_inode_remove_request().

Reported-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Joe Quanaim <jdq@meta.com>
Tested-by: Andrew Steffen <aksteffen@meta.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Fixes: bd37d6fce1 ("NFSv4: Convert nfs_lock_and_join_requests() to use nfs_page_find_head_request()")
Cc: stable@vger.kernel.org
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Trond Myklebust 2025-08-16 07:25:20 -07:00 committed by Greg Kroah-Hartman
parent a9f726bd10
commit 92278ae369
3 changed files with 16 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
fs/nfs/pagelist.c
View File

@ -253,13 +253,14 @@ nfs_page_group_unlock(struct nfs_page *req)
nfs_page_clear_headlock(req);
}
/*
* nfs_page_group_sync_on_bit_locked
/**
* nfs_page_group_sync_on_bit_locked - Test if all requests have @bit set
* @req: request in page group
* @bit: PG_* bit that is used to sync page group
*
* must be called with page group lock held
*/
static bool
nfs_page_group_sync_on_bit_locked(struct nfs_page *req, unsigned int bit)
bool nfs_page_group_sync_on_bit_locked(struct nfs_page *req, unsigned int bit)
{
struct nfs_page *head = req->wb_head;
struct nfs_page *tmp;

29
fs/nfs/write.c
View File

@ -153,20 +153,10 @@ nfs_page_set_inode_ref(struct nfs_page *req, struct inode *inode)
}
}
static int
nfs_cancel_remove_inode(struct nfs_page *req, struct inode *inode)
static void nfs_cancel_remove_inode(struct nfs_page *req, struct inode *inode)
{
int ret;
if (!test_bit(PG_REMOVE, &req->wb_flags))
return 0;
ret = nfs_page_group_lock(req);
if (ret)
return ret;
if (test_and_clear_bit(PG_REMOVE, &req->wb_flags))
nfs_page_set_inode_ref(req, inode);
nfs_page_group_unlock(req);
return 0;
}
/**
@ -585,19 +575,18 @@ retry:
}
}
ret = nfs_page_group_lock(head);
if (ret < 0)
goto out_unlock;
/* Ensure that nobody removed the request before we locked it */
if (head != folio->private) {
nfs_page_group_unlock(head);
nfs_unlock_and_release_request(head);
goto retry;
}
ret = nfs_cancel_remove_inode(head, inode);
if (ret < 0)
goto out_unlock;
ret = nfs_page_group_lock(head);
if (ret < 0)
goto out_unlock;
nfs_cancel_remove_inode(head, inode);
/* lock each request in the page group */
for (subreq = head->wb_this_page;
@ -801,7 +790,8 @@ static void nfs_inode_remove_request(struct nfs_page *req)
{
struct nfs_inode *nfsi = NFS_I(nfs_page_to_inode(req));
if (nfs_page_group_sync_on_bit(req, PG_REMOVE)) {
nfs_page_group_lock(req);
if (nfs_page_group_sync_on_bit_locked(req, PG_REMOVE)) {
struct folio *folio = nfs_page_to_folio(req->wb_head);
struct address_space *mapping = folio->mapping;
@ -812,6 +802,7 @@ static void nfs_inode_remove_request(struct nfs_page *req)
}
spin_unlock(&mapping->i_private_lock);
}
nfs_page_group_unlock(req);
if (test_and_clear_bit(PG_INODE_REF, &req->wb_flags)) {
atomic_long_dec(&nfsi->nrequests);

1
include/linux/nfs_page.h
View File

@ -160,6 +160,7 @@ extern void nfs_join_page_group(struct nfs_page *head,
extern int nfs_page_group_lock(struct nfs_page *);
extern void nfs_page_group_unlock(struct nfs_page *);
extern bool nfs_page_group_sync_on_bit(struct nfs_page *, unsigned int);
extern bool nfs_page_group_sync_on_bit_locked(struct nfs_page *, unsigned int);
extern int nfs_page_set_headlock(struct nfs_page *req);
extern void nfs_page_clear_headlock(struct nfs_page *req);
extern bool nfs_async_iocounter_wait(struct rpc_task *, struct nfs_lock_context *);