Messages in this thread Patch in this message | | | Date | Wed, 12 Jun 2002 11:27:41 -0500 (CDT) | From | Daniel Forrest <> | Subject | [PATCH] lockd hangs during host lookup garbage collection |
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A deadlock occurs under the following sequence:
->nlmsvc_lock calls down(&file->f_sema) ->nlmsvc_create_block ->nlmclnt_lookup_host ->nlm_lookup_host may do garbage collection ->nlm_gc_hosts ->nlmsvc_mark_resources ->nlm_traverse_files action = NLM_ACT_MARK ->nlm_inspect_file loops over all files ->nlmsvc_traverse_blocks calls down(&file->f_sema)
Under heavy load (i.e. >32 client machines locking/unlocking the same NFS mounted file repeatedly) this happens within seconds.
I discussed this with Trond Myklebust a couple of months ago, but the question became one of why f_sema was being used at all. I don't know the answer to that question. Until someone else removes f_sema, the following patch will avoid the problem.
Please apply.
Dan
--- fs/lockd/svclock.c.ORIG Thu Oct 11 09:52:18 2001 +++ fs/lockd/svclock.c Tue Jun 11 17:06:01 2002 @@ -176,8 +176,14 @@ struct nlm_rqst *call; /* Create host handle for callback */ + /* We must up the semaphore in case the host lookup does + * garbage collection (which calls nlmsvc_traverse_blocks), + * but this shouldn't be a problem because nlmsvc_lock has + * to retry the lock after this anyway */ + up(&file->f_sema); host = nlmclnt_lookup_host(&rqstp->rq_addr, rqstp->rq_prot, rqstp->rq_vers); + down(&file->f_sema); if (host == NULL) return NULL;
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