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Subject[PATCH 4.19 137/245] NFS: Fix races nfs_page_group_destroy() vs nfs_destroy_unlinked_subrequests()
Date
From: Trond Myklebust <trond.myklebust@hammerspace.com>

[ Upstream commit 08ca8b21f760c0ed5034a5c122092eec22ccf8f4 ]

When a subrequest is being detached from the subgroup, we want to
ensure that it is not holding the group lock, or in the process
of waiting for the group lock.

Fixes: 5b2b5187fa85 ("NFS: Fix nfs_page_group_destroy() and nfs_lock_and_join_requests() race cases")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/nfs/pagelist.c | 67 +++++++++++++++++++++++++++-------------
fs/nfs/write.c | 10 ++++--
include/linux/nfs_page.h | 2 ++
3 files changed, 55 insertions(+), 24 deletions(-)

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index 5dae7c85d9b6e..2c7d76b4c5e18 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -132,47 +132,70 @@ nfs_async_iocounter_wait(struct rpc_task *task, struct nfs_lock_context *l_ctx)
EXPORT_SYMBOL_GPL(nfs_async_iocounter_wait);

/*
- * nfs_page_group_lock - lock the head of the page group
- * @req - request in group that is to be locked
+ * nfs_page_set_headlock - set the request PG_HEADLOCK
+ * @req: request that is to be locked
*
- * this lock must be held when traversing or modifying the page
- * group list
+ * this lock must be held when modifying req->wb_head
*
* return 0 on success, < 0 on error
*/
int
-nfs_page_group_lock(struct nfs_page *req)
+nfs_page_set_headlock(struct nfs_page *req)
{
- struct nfs_page *head = req->wb_head;
-
- WARN_ON_ONCE(head != head->wb_head);
-
- if (!test_and_set_bit(PG_HEADLOCK, &head->wb_flags))
+ if (!test_and_set_bit(PG_HEADLOCK, &req->wb_flags))
return 0;

- set_bit(PG_CONTENDED1, &head->wb_flags);
+ set_bit(PG_CONTENDED1, &req->wb_flags);
smp_mb__after_atomic();
- return wait_on_bit_lock(&head->wb_flags, PG_HEADLOCK,
+ return wait_on_bit_lock(&req->wb_flags, PG_HEADLOCK,
TASK_UNINTERRUPTIBLE);
}

/*
- * nfs_page_group_unlock - unlock the head of the page group
- * @req - request in group that is to be unlocked
+ * nfs_page_clear_headlock - clear the request PG_HEADLOCK
+ * @req: request that is to be locked
*/
void
-nfs_page_group_unlock(struct nfs_page *req)
+nfs_page_clear_headlock(struct nfs_page *req)
{
- struct nfs_page *head = req->wb_head;
-
- WARN_ON_ONCE(head != head->wb_head);
-
smp_mb__before_atomic();
- clear_bit(PG_HEADLOCK, &head->wb_flags);
+ clear_bit(PG_HEADLOCK, &req->wb_flags);
smp_mb__after_atomic();
- if (!test_bit(PG_CONTENDED1, &head->wb_flags))
+ if (!test_bit(PG_CONTENDED1, &req->wb_flags))
return;
- wake_up_bit(&head->wb_flags, PG_HEADLOCK);
+ wake_up_bit(&req->wb_flags, PG_HEADLOCK);
+}
+
+/*
+ * nfs_page_group_lock - lock the head of the page group
+ * @req: request in group that is to be locked
+ *
+ * this lock must be held when traversing or modifying the page
+ * group list
+ *
+ * return 0 on success, < 0 on error
+ */
+int
+nfs_page_group_lock(struct nfs_page *req)
+{
+ int ret;
+
+ ret = nfs_page_set_headlock(req);
+ if (ret || req->wb_head == req)
+ return ret;
+ return nfs_page_set_headlock(req->wb_head);
+}
+
+/*
+ * nfs_page_group_unlock - unlock the head of the page group
+ * @req: request in group that is to be unlocked
+ */
+void
+nfs_page_group_unlock(struct nfs_page *req)
+{
+ if (req != req->wb_head)
+ nfs_page_clear_headlock(req->wb_head);
+ nfs_page_clear_headlock(req);
}

/*
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 63d20308a9bb7..d419d89b91f7c 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -416,22 +416,28 @@ nfs_destroy_unlinked_subrequests(struct nfs_page *destroy_list,
destroy_list = (subreq->wb_this_page == old_head) ?
NULL : subreq->wb_this_page;

+ /* Note: lock subreq in order to change subreq->wb_head */
+ nfs_page_set_headlock(subreq);
WARN_ON_ONCE(old_head != subreq->wb_head);

/* make sure old group is not used */
subreq->wb_this_page = subreq;
+ subreq->wb_head = subreq;

clear_bit(PG_REMOVE, &subreq->wb_flags);

/* Note: races with nfs_page_group_destroy() */
if (!kref_read(&subreq->wb_kref)) {
/* Check if we raced with nfs_page_group_destroy() */
- if (test_and_clear_bit(PG_TEARDOWN, &subreq->wb_flags))
+ if (test_and_clear_bit(PG_TEARDOWN, &subreq->wb_flags)) {
+ nfs_page_clear_headlock(subreq);
nfs_free_request(subreq);
+ } else
+ nfs_page_clear_headlock(subreq);
continue;
}
+ nfs_page_clear_headlock(subreq);

- subreq->wb_head = subreq;
nfs_release_request(old_head);

if (test_and_clear_bit(PG_INODE_REF, &subreq->wb_flags)) {
diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
index ad69430fd0eb5..5162fc1533c2f 100644
--- a/include/linux/nfs_page.h
+++ b/include/linux/nfs_page.h
@@ -142,6 +142,8 @@ extern void nfs_unlock_and_release_request(struct nfs_page *);
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 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 *);

/*
--
2.25.1


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