Re: [PATCH net-next] packet: Protect packet sk list with mutex (v2)

On Tue, 2012-08-21 at 15:06 +0400, Pavel Emelyanov wrote:
> Change since v1:
> 
> * Fixed inuse counters access spotted by Eric
> 
> In patch eea68e2f (packet: Report socket mclist info via diag module) I've
> introduced a "scheduling in atomic" problem in packet diag module -- the
> socket list is traversed under rcu_read_lock() while performed under it sk
> mclist access requires rtnl lock (i.e. -- mutex) to be taken.
> 
> [152363.820563] BUG: scheduling while atomic: crtools/12517/0x10000002
> [152363.820573] 4 locks held by crtools/12517:
> [152363.820581]  #0:  (sock_diag_mutex){+.+.+.}, at: [<ffffffff81a2dcb5>] sock_diag_rcv+0x1f/0x3e
> [152363.820613]  #1:  (sock_diag_table_mutex){+.+.+.}, at: [<ffffffff81a2de70>] sock_diag_rcv_msg+0xdb/0x11a
> [152363.820644]  #2:  (nlk->cb_mutex){+.+.+.}, at: [<ffffffff81a67d01>] netlink_dump+0x23/0x1ab
> [152363.820693]  #3:  (rcu_read_lock){.+.+..}, at: [<ffffffff81b6a049>] packet_diag_dump+0x0/0x1af
> 
> Similar thing was then re-introduced by further packet diag patches (fanount 
> mutex and pgvec mutex for rings) :(
> 
> Apart from being terribly sorry for the above, I propose to change the packet
> sk list protection from spinlock to mutex. This lock currently protects two
> modifications:
> 
> * sklist
> * prot inuse counters
> 
> The sklist modifications can be just reprotected with mutex since they already
> occur in a sleeping context. The inuse counters modifications are trickier -- the
> __this_cpu_-s are used inside, thus requiring the caller to handle the potential