* Fwd: [PATCH] nfsd: add list_head nf_gc to struct nfsd_file
[not found] <20240710144122.61685-1-youzhong@gmail.com>
@ 2025-01-15 19:48 ` Chuck Lever
2025-01-21 13:35 ` Greg KH
2025-01-16 0:25 ` Sasha Levin
1 sibling, 1 reply; 3+ messages in thread
From: Chuck Lever @ 2025-01-15 19:48 UTC (permalink / raw)
To: stable@vger.kernel.org; +Cc: Linux NFS Mailing List, Youzhong Yang, Jeff Layton
Hi Sasha, Greg -
This is upstream commit 8e6e2ffa6569a205f1805cbaeca143b556581da6. I've
received a request for it to be applied specifically to v5.15.y. Can you
apply it to all LTS kernels back to v5.10 ?
-------- Forwarded Message --------
Subject: [PATCH] nfsd: add list_head nf_gc to struct nfsd_file
Date: Wed, 10 Jul 2024 10:40:35 -0400
From: Youzhong Yang <youzhong@gmail.com>
To: jlayton@kernel.org, chuck.lever@oracle.com,
linux-nfs@vger.kernel.org, youzhong@gmail.com
nfsd_file_put() in one thread can race with another thread doing
garbage collection (running nfsd_file_gc() -> list_lru_walk() ->
nfsd_file_lru_cb()):
* In nfsd_file_put(), nf->nf_ref is 1, so it tries to do
nfsd_file_lru_add().
* nfsd_file_lru_add() returns true (with NFSD_FILE_REFERENCED bit set)
* garbage collector kicks in, nfsd_file_lru_cb() clears REFERENCED
bit and
returns LRU_ROTATE.
* garbage collector kicks in again, nfsd_file_lru_cb() now decrements
nf->nf_ref
to 0, runs nfsd_file_unhash(), removes it from the LRU and adds to
the dispose
list [list_lru_isolate_move(lru, &nf->nf_lru, head)]
* nfsd_file_put() detects NFSD_FILE_HASHED bit is cleared, so it
tries to remove
the 'nf' from the LRU [if (!nfsd_file_lru_remove(nf))]. The 'nf'
has been added
to the 'dispose' list by nfsd_file_lru_cb(), so
nfsd_file_lru_remove(nf) simply
treats it as part of the LRU and removes it, which leads to its
removal from
the 'dispose' list.
* At this moment, 'nf' is unhashed with its nf_ref being 0, and not
on the LRU.
nfsd_file_put() continues its execution [if
(refcount_dec_and_test(&nf->nf_ref))],
as nf->nf_ref is already 0, nf->nf_ref is set to
REFCOUNT_SATURATED, and the 'nf'
gets no chance of being freed.
nfsd_file_put() can also race with nfsd_file_cond_queue():
* In nfsd_file_put(), nf->nf_ref is 1, so it tries to do
nfsd_file_lru_add().
* nfsd_file_lru_add() sets REFERENCED bit and returns true.
* Some userland application runs 'exportfs -f' or something like
that, which triggers
__nfsd_file_cache_purge() -> nfsd_file_cond_queue().
* In nfsd_file_cond_queue(), it runs [if (!nfsd_file_unhash(nf))],
unhash is done
successfully.
* nfsd_file_cond_queue() runs [if (!nfsd_file_get(nf))], now
nf->nf_ref goes to 2.
* nfsd_file_cond_queue() runs [if (nfsd_file_lru_remove(nf))], it
succeeds.
* nfsd_file_cond_queue() runs [if (refcount_sub_and_test(decrement,
&nf->nf_ref))]
(with "decrement" being 2), so the nf->nf_ref goes to 0, the 'nf'
is added to the
dispose list [list_add(&nf->nf_lru, dispose)]
* nfsd_file_put() detects NFSD_FILE_HASHED bit is cleared, so it
tries to remove
the 'nf' from the LRU [if (!nfsd_file_lru_remove(nf))], although
the 'nf' is not
in the LRU, but it is linked in the 'dispose' list,
nfsd_file_lru_remove() simply
treats it as part of the LRU and removes it. This leads to its
removal from
the 'dispose' list!
* Now nf->ref is 0, unhashed. nfsd_file_put() continues its execution
and set
nf->nf_ref to REFCOUNT_SATURATED.
As shown in the above analysis, using nf_lru for both the LRU list and
dispose list
can cause the leaks. This patch adds a new list_head nf_gc in struct
nfsd_file, and uses
it for the dispose list. This does not fix the nfsd_file leaking issue
completely.
Signed-off-by: Youzhong Yang <youzhong@gmail.com>
---
fs/nfsd/filecache.c | 18 ++++++++++--------
fs/nfsd/filecache.h | 1 +
2 files changed, 11 insertions(+), 8 deletions(-)
diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index ad9083ca144b..22ebd7fb8639 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -216,6 +216,7 @@ nfsd_file_alloc(struct net *net, struct inode
*inode, unsigned char need,
return NULL;
INIT_LIST_HEAD(&nf->nf_lru);
+ INIT_LIST_HEAD(&nf->nf_gc);
nf->nf_birthtime = ktime_get();
nf->nf_file = NULL;
nf->nf_cred = get_current_cred();
@@ -393,8 +394,8 @@ nfsd_file_dispose_list(struct list_head *dispose)
struct nfsd_file *nf;
while (!list_empty(dispose)) {
- nf = list_first_entry(dispose, struct nfsd_file, nf_lru);
- list_del_init(&nf->nf_lru);
+ nf = list_first_entry(dispose, struct nfsd_file, nf_gc);
+ list_del_init(&nf->nf_gc);
nfsd_file_free(nf);
}
}
@@ -411,12 +412,12 @@ nfsd_file_dispose_list_delayed(struct list_head
*dispose)
{
while(!list_empty(dispose)) {
struct nfsd_file *nf = list_first_entry(dispose,
- struct nfsd_file, nf_lru);
+ struct nfsd_file, nf_gc);
struct nfsd_net *nn = net_generic(nf->nf_net, nfsd_net_id);
struct nfsd_fcache_disposal *l = nn->fcache_disposal;
spin_lock(&l->lock);
- list_move_tail(&nf->nf_lru, &l->freeme);
+ list_move_tail(&nf->nf_gc, &l->freeme);
spin_unlock(&l->lock);
svc_wake_up(nn->nfsd_serv);
}
@@ -503,7 +504,8 @@ nfsd_file_lru_cb(struct list_head *item, struct
list_lru_one *lru,
/* Refcount went to zero. Unhash it and queue it to the dispose list */
nfsd_file_unhash(nf);
- list_lru_isolate_move(lru, &nf->nf_lru, head);
+ list_lru_isolate(lru, &nf->nf_lru);
+ list_add(&nf->nf_gc, head);
this_cpu_inc(nfsd_file_evictions);
trace_nfsd_file_gc_disposed(nf);
return LRU_REMOVED;
@@ -578,7 +580,7 @@ nfsd_file_cond_queue(struct nfsd_file *nf, struct
list_head *dispose)
/* If refcount goes to 0, then put on the dispose list */
if (refcount_sub_and_test(decrement, &nf->nf_ref)) {
- list_add(&nf->nf_lru, dispose);
+ list_add(&nf->nf_gc, dispose);
trace_nfsd_file_closing(nf);
}
}
@@ -654,8 +656,8 @@ nfsd_file_close_inode_sync(struct inode *inode)
nfsd_file_queue_for_close(inode, &dispose);
while (!list_empty(&dispose)) {
- nf = list_first_entry(&dispose, struct nfsd_file, nf_lru);
- list_del_init(&nf->nf_lru);
+ nf = list_first_entry(&dispose, struct nfsd_file, nf_gc);
+ list_del_init(&nf->nf_gc);
nfsd_file_free(nf);
}
}
diff --git a/fs/nfsd/filecache.h b/fs/nfsd/filecache.h
index c61884def906..3fbec24eea6c 100644
--- a/fs/nfsd/filecache.h
+++ b/fs/nfsd/filecache.h
@@ -44,6 +44,7 @@ struct nfsd_file {
struct nfsd_file_mark *nf_mark;
struct list_head nf_lru;
+ struct list_head nf_gc;
struct rcu_head nf_rcu;
ktime_t nf_birthtime;
};
--
2.45.2
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