On Fri, 22 Aug 2014 18:49:31 -0400 Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> wrote: > Junxiao Bi reports seeing the following deadlock: > > @ crash> bt 1539 > @ PID: 1539 TASK: ffff88178f64a040 CPU: 1 COMMAND: "rpciod/1" > @ #0 [ffff88178f64d2c0] schedule at ffffffff8145833a > @ #1 [ffff88178f64d348] io_schedule at ffffffff8145842c > @ #2 [ffff88178f64d368] sync_page at ffffffff810d8161 > @ #3 [ffff88178f64d378] __wait_on_bit at ffffffff8145895b > @ #4 [ffff88178f64d3b8] wait_on_page_bit at ffffffff810d82fe > @ #5 [ffff88178f64d418] wait_on_page_writeback at ffffffff810e2a1a > @ #6 [ffff88178f64d438] shrink_page_list at ffffffff810e34e1 > @ #7 [ffff88178f64d588] shrink_list at ffffffff810e3dbe > @ #8 [ffff88178f64d6f8] shrink_zone at ffffffff810e425e > @ #9 [ffff88178f64d7b8] do_try_to_free_pages at ffffffff810e4978 > @ #10 [ffff88178f64d828] try_to_free_pages at ffffffff810e4c31 > @ #11 [ffff88178f64d8c8] __alloc_pages_nodemask at ffffffff810de370 This stack trace (from 2.6.32) cannot happen in mainline, though it took me a while to remember/discover exactly why. try_to_free_pages() creates a 'struct scan_control' with ->target_mem_cgroup set to NULL. shrink_page_list() checks ->target_mem_cgroup using global_reclaim() and if it is NULL, wait_on_page_writeback is *not* called. So we can only hit this deadlock if mem-cgroup limits are imposed on a process which is using NFS - which is quite possible but probably not common. The fact that a dead-lock can happen only when memcg limits are imposed seems very fragile. People aren't going to test that case much so there could well be other deadlock possibilities lurking. Mel: might there be some other way we could get out of this deadlock? Could the wait_on_page_writeback() in shrink_page_list() be made a timed-out wait or something? Any other wait out of this deadlock other than setting PF_MEMALLOC_NOIO everywhere? Thanks, NeilBrown > @ #12 [ffff88178f64d978] kmem_getpages at ffffffff8110e18b > @ #13 [ffff88178f64d9a8] fallback_alloc at ffffffff8110e35e > @ #14 [ffff88178f64da08] ____cache_alloc_node at ffffffff8110e51f > @ #15 [ffff88178f64da48] __kmalloc at ffffffff8110efba > @ #16 [ffff88178f64da98] xs_setup_xprt at ffffffffa00a563f [sunrpc] > @ #17 [ffff88178f64dad8] xs_setup_tcp at ffffffffa00a7648 [sunrpc] > @ #18 [ffff88178f64daf8] xprt_create_transport at ffffffffa00a478f [sunrpc] > @ #19 [ffff88178f64db18] rpc_create at ffffffffa00a2d7a [sunrpc] > @ #20 [ffff88178f64dbf8] rpcb_create at ffffffffa00b026b [sunrpc] > @ #21 [ffff88178f64dc98] rpcb_getport_async at ffffffffa00b0c94 [sunrpc] > @ #22 [ffff88178f64ddf8] call_bind at ffffffffa00a11f8 [sunrpc] > @ #23 [ffff88178f64de18] __rpc_execute at ffffffffa00a88ef [sunrpc] > @ #24 [ffff88178f64de58] rpc_async_schedule at ffffffffa00a9187 [sunrpc] > @ #25 [ffff88178f64de78] worker_thread at ffffffff81072ed2 > @ #26 [ffff88178f64dee8] kthread at ffffffff81076df3 > @ #27 [ffff88178f64df48] kernel_thread at ffffffff81012e2a > @ crash> > > Junxiao notes that the problem is not limited to the rpcbind client. In > fact we can trigger the exact same problem when trying to reconnect to > the server, and we find ourselves calling sock_alloc(). > > The following solution should work for all kernels that support the > PF_MEMALLOC_NOIO flag (i.e. Linux 3.9 and newer). > > Link: http://lkml.kernel.org/r/53F6F772.6020708@xxxxxxxxxx > Reported-by: Junxiao Bi <junxiao.bi@xxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx # 3.9+ > Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> > --- > net/sunrpc/sched.c | 5 +++-- > net/sunrpc/xprtsock.c | 15 ++++++++------- > 2 files changed, 11 insertions(+), 9 deletions(-) > > diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c > index 9358c79fd589..ab3aff71ff93 100644 > --- a/net/sunrpc/sched.c > +++ b/net/sunrpc/sched.c > @@ -19,6 +19,7 @@ > #include <linux/spinlock.h> > #include <linux/mutex.h> > #include <linux/freezer.h> > +#include <linux/sched.h> > > #include <linux/sunrpc/clnt.h> > > @@ -821,9 +822,9 @@ void rpc_execute(struct rpc_task *task) > > static void rpc_async_schedule(struct work_struct *work) > { > - current->flags |= PF_FSTRANS; > + current->flags |= PF_FSTRANS | PF_MEMALLOC_NOIO; > __rpc_execute(container_of(work, struct rpc_task, u.tk_work)); > - current->flags &= ~PF_FSTRANS; > + current->flags &= ~(PF_FSTRANS | PF_MEMALLOC_NOIO); > } > > /** > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c > index 43cd89eacfab..1d6d4d84b299 100644 > --- a/net/sunrpc/xprtsock.c > +++ b/net/sunrpc/xprtsock.c > @@ -38,6 +38,7 @@ > #include <linux/sunrpc/svcsock.h> > #include <linux/sunrpc/xprtsock.h> > #include <linux/file.h> > +#include <linux/sched.h> > #ifdef CONFIG_SUNRPC_BACKCHANNEL > #include <linux/sunrpc/bc_xprt.h> > #endif > @@ -1927,7 +1928,7 @@ static int xs_local_setup_socket(struct sock_xprt *transport) > struct socket *sock; > int status = -EIO; > > - current->flags |= PF_FSTRANS; > + current->flags |= PF_FSTRANS | PF_MEMALLOC_NOIO; > > clear_bit(XPRT_CONNECTION_ABORT, &xprt->state); > status = __sock_create(xprt->xprt_net, AF_LOCAL, > @@ -1968,7 +1969,7 @@ static int xs_local_setup_socket(struct sock_xprt *transport) > out: > xprt_clear_connecting(xprt); > xprt_wake_pending_tasks(xprt, status); > - current->flags &= ~PF_FSTRANS; > + current->flags &= ~(PF_FSTRANS | PF_MEMALLOC_NOIO); > return status; > } > > @@ -2071,7 +2072,7 @@ static void xs_udp_setup_socket(struct work_struct *work) > struct socket *sock = transport->sock; > int status = -EIO; > > - current->flags |= PF_FSTRANS; > + current->flags |= PF_FSTRANS | PF_MEMALLOC_NOIO; > > /* Start by resetting any existing state */ > xs_reset_transport(transport); > @@ -2092,7 +2093,7 @@ static void xs_udp_setup_socket(struct work_struct *work) > out: > xprt_clear_connecting(xprt); > xprt_wake_pending_tasks(xprt, status); > - current->flags &= ~PF_FSTRANS; > + current->flags &= ~(PF_FSTRANS | PF_MEMALLOC_NOIO); > } > > /* > @@ -2229,7 +2230,7 @@ static void xs_tcp_setup_socket(struct work_struct *work) > struct rpc_xprt *xprt = &transport->xprt; > int status = -EIO; > > - current->flags |= PF_FSTRANS; > + current->flags |= PF_FSTRANS | PF_MEMALLOC_NOIO; > > if (!sock) { > clear_bit(XPRT_CONNECTION_ABORT, &xprt->state); > @@ -2276,7 +2277,7 @@ static void xs_tcp_setup_socket(struct work_struct *work) > case -EINPROGRESS: > case -EALREADY: > xprt_clear_connecting(xprt); > - current->flags &= ~PF_FSTRANS; > + current->flags &= ~(PF_FSTRANS | PF_MEMALLOC_NOIO); > return; > case -EINVAL: > /* Happens, for instance, if the user specified a link > @@ -2294,7 +2295,7 @@ out_eagain: > out: > xprt_clear_connecting(xprt); > xprt_wake_pending_tasks(xprt, status); > - current->flags &= ~PF_FSTRANS; > + current->flags &= ~(PF_FSTRANS | PF_MEMALLOC_NOIO); > } > > /**
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