Date: Sat, 4 May 2013 21:56:40 +0000 (UTC) From: Rick Macklem <rmacklem@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-9@freebsd.org Subject: svn commit: r250257 - in stable/9/sys: fs/nfsclient nfsclient Message-ID: <201305042156.r44Luexb063485@svn.freebsd.org>
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Author: rmacklem Date: Sat May 4 21:56:39 2013 New Revision: 250257 URL: http://svnweb.freebsd.org/changeset/base/250257 Log: MFC: r249623 Both NFS clients can deadlock when using the "rdirplus" mount option. This can occur when an nfsiod thread that already holds a buffer lock attempts to acquire a vnode lock on an entry in the directory (a LOR) when another thread holding the vnode lock is waiting on an nfsiod thread. This patch avoids the deadlock by disabling readahead for this case, so the nfsiod threads never do readdirplus. Since readaheads for directories need the directory offset cookie from the previous read, they cannot normally happen in parallel. As such, testing by jhb@ and myself didn't find any performance degredation when this patch is applied. If there is a case where this results in a significant performance degradation, mounting without the "rdirplus" option can be done to re-enable readahead for directories. Modified: stable/9/sys/fs/nfsclient/nfs_clbio.c stable/9/sys/nfsclient/nfs_bio.c Directory Properties: stable/9/sys/ (props changed) stable/9/sys/fs/ (props changed) Modified: stable/9/sys/fs/nfsclient/nfs_clbio.c ============================================================================== --- stable/9/sys/fs/nfsclient/nfs_clbio.c Sat May 4 21:36:47 2013 (r250256) +++ stable/9/sys/fs/nfsclient/nfs_clbio.c Sat May 4 21:56:39 2013 (r250257) @@ -1401,10 +1401,18 @@ ncl_asyncio(struct nfsmount *nmp, struct * Commits are usually short and sweet so lets save some cpu and * leave the async daemons for more important rpc's (such as reads * and writes). + * + * Readdirplus RPCs do vget()s to acquire the vnodes for entries + * in the directory in order to update attributes. This can deadlock + * with another thread that is waiting for async I/O to be done by + * an nfsiod thread while holding a lock on one of these vnodes. + * To avoid this deadlock, don't allow the async nfsiod threads to + * perform Readdirplus RPCs. */ mtx_lock(&ncl_iod_mutex); - if (bp->b_iocmd == BIO_WRITE && (bp->b_flags & B_NEEDCOMMIT) && - (nmp->nm_bufqiods > ncl_numasync / 2)) { + if ((bp->b_iocmd == BIO_WRITE && (bp->b_flags & B_NEEDCOMMIT) && + (nmp->nm_bufqiods > ncl_numasync / 2)) || + (bp->b_vp->v_type == VDIR && (nmp->nm_flag & NFSMNT_RDIRPLUS))) { mtx_unlock(&ncl_iod_mutex); return(EIO); } Modified: stable/9/sys/nfsclient/nfs_bio.c ============================================================================== --- stable/9/sys/nfsclient/nfs_bio.c Sat May 4 21:36:47 2013 (r250256) +++ stable/9/sys/nfsclient/nfs_bio.c Sat May 4 21:56:39 2013 (r250257) @@ -1344,10 +1344,18 @@ nfs_asyncio(struct nfsmount *nmp, struct * Commits are usually short and sweet so lets save some cpu and * leave the async daemons for more important rpc's (such as reads * and writes). + * + * Readdirplus RPCs do vget()s to acquire the vnodes for entries + * in the directory in order to update attributes. This can deadlock + * with another thread that is waiting for async I/O to be done by + * an nfsiod thread while holding a lock on one of these vnodes. + * To avoid this deadlock, don't allow the async nfsiod threads to + * perform Readdirplus RPCs. */ mtx_lock(&nfs_iod_mtx); - if (bp->b_iocmd == BIO_WRITE && (bp->b_flags & B_NEEDCOMMIT) && - (nmp->nm_bufqiods > nfs_numasync / 2)) { + if ((bp->b_iocmd == BIO_WRITE && (bp->b_flags & B_NEEDCOMMIT) && + (nmp->nm_bufqiods > nfs_numasync / 2)) || + (bp->b_vp->v_type == VDIR && (nmp->nm_flag & NFSMNT_RDIRPLUS))) { mtx_unlock(&nfs_iod_mtx); return(EIO); }
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