| Message ID | 20140416040336.10604.60493.stgit@notabene.brown (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Apr 16, 2014 at 02:03:36PM +1000, NeilBrown wrote: > If a localhost mount is present, then it is easy to deadlock NFS by > nfsd entering direct reclaim and calling nfs_release_page() which > requires nfsd to perform an fsync() (which it cannot do because it is > reclaiming memory). > > By setting PF_FSTRANS we stop the memory allocator from ever > attempting any FS operation would could deadlock. > > We need this flag set for any thread which is handling a request from > the local host, but we also need to always have it for at least 1 or 2 > threads so that we don't end up with all threads blocked in allocation. > > When we set PF_FSTRANS we also tell lockdep that we are handling > reclaim so that it can detect deadlocks for us. > > Signed-off-by: NeilBrown <neilb@suse.de> > --- > fs/nfsd/nfssvc.c | 18 ++++++++++++++++++ > include/linux/sunrpc/svc.h | 1 + > net/sunrpc/svc.c | 6 ++++++ > 3 files changed, 25 insertions(+) > > diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c > index 9a4a5f9e7468..6af8bc2daf7d 100644 > --- a/fs/nfsd/nfssvc.c > +++ b/fs/nfsd/nfssvc.c > @@ -565,6 +565,8 @@ nfsd(void *vrqstp) > struct svc_xprt *perm_sock = list_entry(rqstp->rq_server->sv_permsocks.next, typeof(struct svc_xprt), xpt_list); > struct net *net = perm_sock->xpt_net; > int err; > + unsigned int pflags = 0; > + gfp_t reclaim_state = 0; > > /* Lock module and set up kernel thread */ > mutex_lock(&nfsd_mutex); > @@ -611,14 +613,30 @@ nfsd(void *vrqstp) > ; > if (err == -EINTR) > break; > + if (rqstp->rq_local && !current_test_flags(PF_FSTRANS)) { > + current_set_flags_nested(&pflags, PF_FSTRANS); > + atomic_inc(&rqstp->rq_pool->sp_nr_fstrans); > + reclaim_state = lockdep_set_current_reclaim_state(GFP_KERNEL); > + } > validate_process_creds(); > svc_process(rqstp); > validate_process_creds(); > + if (current_test_flags(PF_FSTRANS) && > + atomic_dec_if_positive(&rqstp->rq_pool->sp_nr_fstrans) >= 0) { Yuck, that function has horrible semantics :/ Not your fault though. > + current_restore_flags_nested(&pflags, PF_FSTRANS); > + lockdep_restore_current_reclaim_state(reclaim_state); > + } Not really knowing much about NFS anymore (all I did know seems to have bitrotten) the above looks ok I suppose. Refcounting that task state in something !task_struct feels weird though. > } > > /* Clear signals before calling svc_exit_thread() */ > flush_signals(current); > > + if (current_test_flags(PF_FSTRANS)) { > + current_restore_flags_nested(&pflags, PF_FSTRANS); > + lockdep_restore_current_reclaim_state(reclaim_state); > + atomic_dec(&rqstp->rq_pool->sp_nr_fstrans); > + } > + > mutex_lock(&nfsd_mutex); > nfsdstats.th_cnt --; > > diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h > index a0dbbd1e00e9..4b274aba51dd 100644 > --- a/include/linux/sunrpc/svc.h > +++ b/include/linux/sunrpc/svc.h > @@ -48,6 +48,7 @@ struct svc_pool { > struct list_head sp_threads; /* idle server threads */ > struct list_head sp_sockets; /* pending sockets */ > unsigned int sp_nrthreads; /* # of threads in pool */ > + atomic_t sp_nr_fstrans; /* # threads with PF_FSTRANS */ > struct list_head sp_all_threads; /* all server threads */ > struct svc_pool_stats sp_stats; /* statistics on pool operation */ > int sp_task_pending;/* has pending task */ > diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c > index 5de6801cd924..8b13f35b6cbb 100644 > --- a/net/sunrpc/svc.c > +++ b/net/sunrpc/svc.c > @@ -477,6 +477,12 @@ __svc_create(struct svc_program *prog, unsigned int bufsize, int npools, > INIT_LIST_HEAD(&pool->sp_threads); > INIT_LIST_HEAD(&pool->sp_sockets); > INIT_LIST_HEAD(&pool->sp_all_threads); > + /* The number of threads with PF_FSTRANS set > + * should never be reduced below 2, except when > + * threads exit. So we use atomic_dec_if_positive() > + * on this value. > + */ > + atomic_set(&pool->sp_nr_fstrans, -2); Its not my code, but that's not the recommended multi-line comment style. > spin_lock_init(&pool->sp_lock); > } > > > -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c index 9a4a5f9e7468..6af8bc2daf7d 100644 --- a/fs/nfsd/nfssvc.c +++ b/fs/nfsd/nfssvc.c @@ -565,6 +565,8 @@ nfsd(void *vrqstp) struct svc_xprt *perm_sock = list_entry(rqstp->rq_server->sv_permsocks.next, typeof(struct svc_xprt), xpt_list); struct net *net = perm_sock->xpt_net; int err; + unsigned int pflags = 0; + gfp_t reclaim_state = 0; /* Lock module and set up kernel thread */ mutex_lock(&nfsd_mutex); @@ -611,14 +613,30 @@ nfsd(void *vrqstp) ; if (err == -EINTR) break; + if (rqstp->rq_local && !current_test_flags(PF_FSTRANS)) { + current_set_flags_nested(&pflags, PF_FSTRANS); + atomic_inc(&rqstp->rq_pool->sp_nr_fstrans); + reclaim_state = lockdep_set_current_reclaim_state(GFP_KERNEL); + } validate_process_creds(); svc_process(rqstp); validate_process_creds(); + if (current_test_flags(PF_FSTRANS) && + atomic_dec_if_positive(&rqstp->rq_pool->sp_nr_fstrans) >= 0) { + current_restore_flags_nested(&pflags, PF_FSTRANS); + lockdep_restore_current_reclaim_state(reclaim_state); + } } /* Clear signals before calling svc_exit_thread() */ flush_signals(current); + if (current_test_flags(PF_FSTRANS)) { + current_restore_flags_nested(&pflags, PF_FSTRANS); + lockdep_restore_current_reclaim_state(reclaim_state); + atomic_dec(&rqstp->rq_pool->sp_nr_fstrans); + } + mutex_lock(&nfsd_mutex); nfsdstats.th_cnt --; diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h index a0dbbd1e00e9..4b274aba51dd 100644 --- a/include/linux/sunrpc/svc.h +++ b/include/linux/sunrpc/svc.h @@ -48,6 +48,7 @@ struct svc_pool { struct list_head sp_threads; /* idle server threads */ struct list_head sp_sockets; /* pending sockets */ unsigned int sp_nrthreads; /* # of threads in pool */ + atomic_t sp_nr_fstrans; /* # threads with PF_FSTRANS */ struct list_head sp_all_threads; /* all server threads */ struct svc_pool_stats sp_stats; /* statistics on pool operation */ int sp_task_pending;/* has pending task */ diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c index 5de6801cd924..8b13f35b6cbb 100644 --- a/net/sunrpc/svc.c +++ b/net/sunrpc/svc.c @@ -477,6 +477,12 @@ __svc_create(struct svc_program *prog, unsigned int bufsize, int npools, INIT_LIST_HEAD(&pool->sp_threads); INIT_LIST_HEAD(&pool->sp_sockets); INIT_LIST_HEAD(&pool->sp_all_threads); + /* The number of threads with PF_FSTRANS set + * should never be reduced below 2, except when + * threads exit. So we use atomic_dec_if_positive() + * on this value. + */ + atomic_set(&pool->sp_nr_fstrans, -2); spin_lock_init(&pool->sp_lock); }
If a localhost mount is present, then it is easy to deadlock NFS by nfsd entering direct reclaim and calling nfs_release_page() which requires nfsd to perform an fsync() (which it cannot do because it is reclaiming memory). By setting PF_FSTRANS we stop the memory allocator from ever attempting any FS operation would could deadlock. We need this flag set for any thread which is handling a request from the local host, but we also need to always have it for at least 1 or 2 threads so that we don't end up with all threads blocked in allocation. When we set PF_FSTRANS we also tell lockdep that we are handling reclaim so that it can detect deadlocks for us. Signed-off-by: NeilBrown <neilb@suse.de> --- fs/nfsd/nfssvc.c | 18 ++++++++++++++++++ include/linux/sunrpc/svc.h | 1 + net/sunrpc/svc.c | 6 ++++++ 3 files changed, 25 insertions(+) -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html