From: NeilBrown Date: Sun, 15 Sep 2024 23:45:40 +0000 (+1000) Subject: sunrpc: allow svc threads to fail initialisation cleanly X-Git-Tag: v6.12-rc1~97^2~41 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=3391fc92db8e761f1a2df5612fcb999dac6bc00a;p=thirdparty%2Fkernel%2Flinux.git sunrpc: allow svc threads to fail initialisation cleanly If an svc thread needs to perform some initialisation that might fail, it has no good way to handle the failure. Before the thread can exit it must call svc_exit_thread(), but that requires the service mutex to be held. The thread cannot simply take the mutex as that could deadlock if there is a concurrent attempt to shut down all threads (which is unlikely, but not impossible). nfsd currently call svc_exit_thread() unprotected in the unlikely event that unshare_fs_struct() fails. We can clean this up by introducing svc_thread_init_status() by which an svc thread can report whether initialisation has succeeded. If it has, it continues normally into the action loop. If it has not, svc_thread_init_status() immediately aborts the thread. svc_start_kthread() waits for either of these to happen, and calls svc_exit_thread() (under the mutex) if the thread aborted. Signed-off-by: NeilBrown Reviewed-by: Jeff Layton Signed-off-by: Chuck Lever --- diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c index 71713309967d3..4ec22c2f2ea3c 100644 --- a/fs/lockd/svc.c +++ b/fs/lockd/svc.c @@ -124,6 +124,8 @@ lockd(void *vrqstp) struct net *net = &init_net; struct lockd_net *ln = net_generic(net, lockd_net_id); + svc_thread_init_status(rqstp, 0); + /* try_to_freeze() is called from svc_recv() */ set_freezable(); diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c index 8adfcd4c8c1a0..6cf92498a5ac6 100644 --- a/fs/nfs/callback.c +++ b/fs/nfs/callback.c @@ -76,6 +76,8 @@ nfs4_callback_svc(void *vrqstp) { struct svc_rqst *rqstp = vrqstp; + svc_thread_init_status(rqstp, 0); + set_freezable(); while (!svc_thread_should_stop(rqstp)) diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c index b1dc3404173b3..3fb6c8c9a2f0d 100644 --- a/fs/nfsd/nfssvc.c +++ b/fs/nfsd/nfssvc.c @@ -873,11 +873,9 @@ nfsd(void *vrqstp) /* At this point, the thread shares current->fs * with the init process. We need to create files with the - * umask as defined by the client instead of init's umask. */ - if (unshare_fs_struct() < 0) { - printk("Unable to start nfsd thread: out of memory\n"); - goto out; - } + * umask as defined by the client instead of init's umask. + */ + svc_thread_init_status(rqstp, unshare_fs_struct()); current->fs->umask = 0; @@ -899,7 +897,6 @@ nfsd(void *vrqstp) atomic_dec(&nfsd_th_cnt); -out: /* Release the thread */ svc_exit_thread(rqstp); return 0; diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h index 99e9345d829e8..c419a61f60e53 100644 --- a/include/linux/sunrpc/svc.h +++ b/include/linux/sunrpc/svc.h @@ -21,6 +21,7 @@ #include #include #include +#include /* * @@ -232,6 +233,11 @@ struct svc_rqst { struct net *rq_bc_net; /* pointer to backchannel's * net namespace */ + + int rq_err; /* Thread sets this to inidicate + * initialisation success. + */ + unsigned long bc_to_initval; unsigned int bc_to_retries; void ** rq_lease_breaker; /* The v4 client breaking a lease */ @@ -305,6 +311,31 @@ static inline bool svc_thread_should_stop(struct svc_rqst *rqstp) return test_bit(RQ_VICTIM, &rqstp->rq_flags); } +/** + * svc_thread_init_status - report whether thread has initialised successfully + * @rqstp: the thread in question + * @err: errno code + * + * After performing any initialisation that could fail, and before starting + * normal work, each sunrpc svc_thread must call svc_thread_init_status() + * with an appropriate error, or zero. + * + * If zero is passed, the thread is ready and must continue until + * svc_thread_should_stop() returns true. If a non-zero error is passed + * the call will not return - the thread will exit. + */ +static inline void svc_thread_init_status(struct svc_rqst *rqstp, int err) +{ + rqstp->rq_err = err; + /* memory barrier ensures assignment to error above is visible before + * waitqueue_active() test below completes. + */ + smp_mb(); + wake_up_var(&rqstp->rq_err); + if (err) + kthread_exit(1); +} + struct svc_deferred_req { u32 prot; /* protocol (UDP or TCP) */ struct svc_xprt *xprt; diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c index 17f0f59c068ff..9aff845196ce7 100644 --- a/net/sunrpc/svc.c +++ b/net/sunrpc/svc.c @@ -706,6 +706,8 @@ svc_prepare_thread(struct svc_serv *serv, struct svc_pool *pool, int node) if (!svc_init_buffer(rqstp, serv->sv_max_mesg, node)) goto out_enomem; + rqstp->rq_err = -EAGAIN; /* No error yet */ + serv->sv_nrthreads += 1; pool->sp_nrthreads += 1; @@ -792,6 +794,7 @@ svc_start_kthreads(struct svc_serv *serv, struct svc_pool *pool, int nrservs) struct svc_pool *chosen_pool; unsigned int state = serv->sv_nrthreads-1; int node; + int err; do { nrservs--; @@ -814,6 +817,13 @@ svc_start_kthreads(struct svc_serv *serv, struct svc_pool *pool, int nrservs) svc_sock_update_bufs(serv); wake_up_process(task); + + wait_var_event(&rqstp->rq_err, rqstp->rq_err != -EAGAIN); + err = rqstp->rq_err; + if (err) { + svc_exit_thread(rqstp); + return err; + } } while (nrservs > 0); return 0;