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NFS: Fix races nfs_page_group_destroy() vs nfs_destroy_unlinked_subrequests()

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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: 5b2b5187fa ("NFS: Fix nfs_page_group_destroy() and nfs_lock_and_join_requests() race cases")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
This commit is contained in:
Trond Myklebust
2020-04-01 13:04:49 -04:00
parent add42de317
commit 08ca8b21f7
3 changed files with 55 additions and 24 deletions
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10
fs/nfs/write.c
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@@ -428,22 +428,28 @@ 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)) {