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nfsd: drop st_mutex before calling move_to_close_lru()

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move_to_close_lru() is currently called with ->st_mutex held.
This can lead to a deadlock as move_to_close_lru() waits for sc_count to
drop to 2, and some threads holding a reference might be waiting for the
mutex.  These references will never be dropped so sc_count will never
reach 2.

There can be no harm in dropping ->st_mutex before
move_to_close_lru() because the only place that takes the mutex is
nfsd4_lock_ol_stateid(), and it quickly aborts if sc_type is
NFS4_CLOSED_STID, which it will be before move_to_close_lru() is called.

See also
 https://lore.kernel.org/lkml/4dd1fe21e11344e5969bb112e954affb@jd.com/T/
where this problem was raised but not successfully resolved.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
NeilBrown 2024-04-08 12:09:18 +10:00 committed by Chuck Lever
parent eec7620800
commit 56c35f43ee
1 changed files with 7 additions and 4 deletions
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11
fs/nfsd/nfs4state.c
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@ -7357,7 +7357,7 @@ out:
return status;
}
static void nfsd4_close_open_stateid(struct nfs4_ol_stateid *s)
static bool nfsd4_close_open_stateid(struct nfs4_ol_stateid *s)
{
struct nfs4_client *clp = s->st_stid.sc_client;
bool unhashed;
@ -7374,11 +7374,11 @@ static void nfsd4_close_open_stateid(struct nfs4_ol_stateid *s)
list_for_each_entry(stp, &reaplist, st_locks)
nfs4_free_cpntf_statelist(clp->net, &stp->st_stid);
free_ol_stateid_reaplist(&reaplist);
return false;
} else {
spin_unlock(&clp->cl_lock);
free_ol_stateid_reaplist(&reaplist);
if (unhashed)
move_to_close_lru(s, clp->net);
return unhashed;
}
}
@ -7394,6 +7394,7 @@ nfsd4_close(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
struct nfs4_ol_stateid *stp;
struct net *net = SVC_NET(rqstp);
struct nfsd_net *nn = net_generic(net, nfsd_net_id);
bool need_move_to_close_list;
dprintk("NFSD: nfsd4_close on file %pd\n",
cstate->current_fh.fh_dentry);
@ -7418,8 +7419,10 @@ nfsd4_close(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
*/
nfs4_inc_and_copy_stateid(&close->cl_stateid, &stp->st_stid);
nfsd4_close_open_stateid(stp);
need_move_to_close_list = nfsd4_close_open_stateid(stp);
mutex_unlock(&stp->st_mutex);
if (need_move_to_close_list)
move_to_close_lru(stp, net);
/* v4.1+ suggests that we send a special stateid in here, since the
* clients should just ignore this anyway. Since this is not useful