On Sat, Jul 23, 2016 at 11:52:23AM +0200, Vegard Nossum wrote: > seq_read() can call ->start() twice on the same iterator more than once > (e.g. once through traverse() and once in seq_read() itself). But when traverse() returns the error, it goes to Done label, skipping the call to ->start() from seq_read(), or am I missing something? Though yes, if sctp_ht_iter memory is actually re-used without initializting between seq_read()s, it triggers the issue you described. How did you trigger this, reading after an error on the file descriptor? > > We should initialize sctp_ht_iter::start_fail to zero if ->start() > succeeds, otherwise it's possible that we leave an old value of 1 there, > which will cause ->stop() to not call sctp_transport_walk_stop(), which > causes all sorts of problems like not calling rcu_read_unlock() (and > preempt_enable()), eventually leading to more warnings like this: > > BUG: sleeping function called from invalid context at mm/slab.h:388 > in_atomic(): 0, irqs_disabled(): 0, pid: 16551, name: trinity-c2 > Preemption disabled at:[<ffffffff819bceb6>] rhashtable_walk_start+0x46/0x150 > > [<ffffffff81149abb>] preempt_count_add+0x1fb/0x280 > [<ffffffff83295892>] _raw_spin_lock+0x12/0x40 > [<ffffffff819bceb6>] rhashtable_walk_start+0x46/0x150 > [<ffffffff82ec665f>] sctp_transport_walk_start+0x2f/0x60 > [<ffffffff82edda1d>] sctp_transport_seq_start+0x4d/0x150 > [<ffffffff81439e50>] traverse+0x170/0x850 > [<ffffffff8143aeec>] seq_read+0x7cc/0x1180 > [<ffffffff814f996c>] proc_reg_read+0xbc/0x180 > [<ffffffff813d0384>] do_loop_readv_writev+0x134/0x210 > [<ffffffff813d2a95>] do_readv_writev+0x565/0x660 > [<ffffffff813d6857>] vfs_readv+0x67/0xa0 > [<ffffffff813d6c16>] do_preadv+0x126/0x170 > [<ffffffff813d710c>] SyS_preadv+0xc/0x10 > [<ffffffff8100334c>] do_syscall_64+0x19c/0x410 > [<ffffffff83296225>] return_from_SYSCALL_64+0x0/0x6a > [<ffffffffffffffff>] 0xffffffffffffffff > > (Notice that this is a subtly different stacktrace from the previous bug > I reported.) > > Cc: Xin Long <lucien.xin@xxxxxxxxx> > Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> > Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx> > --- > net/sctp/proc.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/net/sctp/proc.c b/net/sctp/proc.c > index 4cb5aed..ef8ba77 100644 > --- a/net/sctp/proc.c > +++ b/net/sctp/proc.c > @@ -293,6 +293,7 @@ static void *sctp_transport_seq_start(struct seq_file *seq, loff_t *pos) > return ERR_PTR(err); > } > > + iter->start_fail = 0; > return sctp_transport_get_idx(seq_file_net(seq), &iter->hti, *pos); > } > > -- > 1.9.1 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-sctp" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
