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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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67
fs/nfs/pagelist.c
View File

@ -132,9 +132,44 @@ nfs_async_iocounter_wait(struct rpc_task *task, struct nfs_lock_context *l_ctx)
}
EXPORT_SYMBOL_GPL(nfs_async_iocounter_wait);
/*
* nfs_page_set_headlock - set the request PG_HEADLOCK
* @req: request that is to be locked
*
* this lock must be held when modifying req->wb_head
*
* return 0 on success, < 0 on error
*/
int
nfs_page_set_headlock(struct nfs_page *req)
{
if (!test_and_set_bit(PG_HEADLOCK, &req->wb_flags))
return 0;
set_bit(PG_CONTENDED1, &req->wb_flags);
smp_mb__after_atomic();
return wait_on_bit_lock(&req->wb_flags, PG_HEADLOCK,
TASK_UNINTERRUPTIBLE);
}
/*
* nfs_page_clear_headlock - clear the request PG_HEADLOCK
* @req: request that is to be locked
*/
void
nfs_page_clear_headlock(struct nfs_page *req)
{
smp_mb__before_atomic();
clear_bit(PG_HEADLOCK, &req->wb_flags);
smp_mb__after_atomic();
if (!test_bit(PG_CONTENDED1, &req->wb_flags))
return;
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
* @req: request in group that is to be locked
*
* this lock must be held when traversing or modifying the page
* group list
@ -144,36 +179,24 @@ EXPORT_SYMBOL_GPL(nfs_async_iocounter_wait);
int
nfs_page_group_lock(struct nfs_page *req)
{
struct nfs_page *head = req->wb_head;
int ret;
WARN_ON_ONCE(head != head->wb_head);
if (!test_and_set_bit(PG_HEADLOCK, &head->wb_flags))
return 0;
set_bit(PG_CONTENDED1, &head->wb_flags);
smp_mb__after_atomic();
return wait_on_bit_lock(&head->wb_flags, PG_HEADLOCK,
TASK_UNINTERRUPTIBLE);
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
* @req: request in group that is to be unlocked
*/
void
nfs_page_group_unlock(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);
smp_mb__after_atomic();
if (!test_bit(PG_CONTENDED1, &head->wb_flags))
return;
wake_up_bit(&head->wb_flags, PG_HEADLOCK);
if (req != req->wb_head)
nfs_page_clear_headlock(req->wb_head);
nfs_page_clear_headlock(req);
}
/*

10
fs/nfs/write.c
View File

@ -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)) {

2
include/linux/nfs_page.h
View File

@ -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 *);
/*