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    Subject[PATCH 5.5 01/46] ipv4: fix a RCU-list lock in fib_triestat_seq_show
    Date
    From: Qian Cai <cai@lca.pw>

    [ Upstream commit fbe4e0c1b298b4665ee6915266c9d6c5b934ef4a ]

    fib_triestat_seq_show() calls hlist_for_each_entry_rcu(tb, head,
    tb_hlist) without rcu_read_lock() will trigger a warning,

    net/ipv4/fib_trie.c:2579 RCU-list traversed in non-reader section!!

    other info that might help us debug this:

    rcu_scheduler_active = 2, debug_locks = 1
    1 lock held by proc01/115277:
    #0: c0000014507acf00 (&p->lock){+.+.}-{3:3}, at: seq_read+0x58/0x670

    Call Trace:
    dump_stack+0xf4/0x164 (unreliable)
    lockdep_rcu_suspicious+0x140/0x164
    fib_triestat_seq_show+0x750/0x880
    seq_read+0x1a0/0x670
    proc_reg_read+0x10c/0x1b0
    __vfs_read+0x3c/0x70
    vfs_read+0xac/0x170
    ksys_read+0x7c/0x140
    system_call+0x5c/0x68

    Fix it by adding a pair of rcu_read_lock/unlock() and use
    cond_resched_rcu() to avoid the situation where walking of a large
    number of items may prevent scheduling for a long time.

    Signed-off-by: Qian Cai <cai@lca.pw>
    Reviewed-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv4/fib_trie.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/net/ipv4/fib_trie.c
    +++ b/net/ipv4/fib_trie.c
    @@ -2473,6 +2473,7 @@ static int fib_triestat_seq_show(struct
    " %zd bytes, size of tnode: %zd bytes.\n",
    LEAF_SIZE, TNODE_SIZE(0));

    + rcu_read_lock();
    for (h = 0; h < FIB_TABLE_HASHSZ; h++) {
    struct hlist_head *head = &net->ipv4.fib_table_hash[h];
    struct fib_table *tb;
    @@ -2492,7 +2493,9 @@ static int fib_triestat_seq_show(struct
    trie_show_usage(seq, t->stats);
    #endif
    }
    + cond_resched_rcu();
    }
    + rcu_read_unlock();

    return 0;
    }

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