lkml.org 
[lkml]   [2020]   [May]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH net 2/2 RESEND] ipmr: Add lockdep expression to ipmr_for_each_table macro
    On Sat,  9 May 2020 12:52:44 +0530 Amol Grover wrote:
    > ipmr_for_each_table() uses list_for_each_entry_rcu() for
    > traversing outside of an RCU read-side critical section but
    > under the protection of pernet_ops_rwsem. Hence add the
    > corresponding lockdep expression to silence the following
    > false-positive warning at boot:

    Thanks for the fix, the warning has been annoying me as well!

    > [ 0.645292] =============================
    > [ 0.645294] WARNING: suspicious RCU usage
    > [ 0.645296] 5.5.4-stable #17 Not tainted
    > [ 0.645297] -----------------------------
    > [ 0.645299] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!

    please provide a fuller stack trace, it would have helped the review

    > Signed-off-by: Amol Grover <frextrite@gmail.com>
    > ---
    > net/ipv4/ipmr.c | 7 ++++---
    > 1 file changed, 4 insertions(+), 3 deletions(-)
    >
    > diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
    > index 99c864eb6e34..950ffe9943da 100644
    > --- a/net/ipv4/ipmr.c
    > +++ b/net/ipv4/ipmr.c
    > @@ -109,9 +109,10 @@ static void mroute_clean_tables(struct mr_table *mrt, int flags);
    > static void ipmr_expire_process(struct timer_list *t);
    >
    > #ifdef CONFIG_IP_MROUTE_MULTIPLE_TABLES
    > -#define ipmr_for_each_table(mrt, net) \
    > - list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
    > - lockdep_rtnl_is_held())
    > +#define ipmr_for_each_table(mrt, net) \
    > + list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
    > + lockdep_rtnl_is_held() || \
    > + lockdep_is_held(&pernet_ops_rwsem))

    This is a strange condition, IMHO. How can we be fine with either
    lock.. This is supposed to be the writer side lock, one can't have
    two writer side locks..

    I think what is happening is this:

    ipmr_net_init() -> ipmr_rules_init() -> ipmr_new_table()

    ipmr_new_table() returns an existing table if there is one, but
    obviously none can exist at init. So a better fix would be:

    #define ipmr_for_each_table(mrt, net) \
    list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
    lockdep_rtnl_is_held() || \
    list_empty(&net->ipv4.mr_tables))

    Thoughts?

    \
     
     \ /
      Last update: 2020-05-09 23:20    [W:5.800 / U:0.412 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site