xfs: reduce ilock roundtrips in xfs_qm_vop_dqalloc

xfs_qm_vop_dqalloc only needs the (exclusive) ilock for attaching dquots
to the inode if not done so yet.  All the other locks don't touch the inode
and don't need the ilock - the i_rwsem / iolock protects against changes
to the IDs while we are in a method, and the ilock would not help because
dropping it for the dqget calls would be racy anyway.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index a81b8b7a4e4f528dfb579ade024f65f4ed5ac85b..95be67ac6eb424faa905af2dcf8b3ce84130f45b 100644 (file)
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -1861,16 +1861,12 @@ xfs_qm_vop_dqalloc(
        struct xfs_dquot        *gq = NULL;
        struct xfs_dquot        *pq = NULL;
        int                     error;
-       uint                    lockflags;
 
        if (!XFS_IS_QUOTA_ON(mp))
                return 0;
 
        ASSERT(!xfs_is_metadir_inode(ip));
 
-       lockflags = XFS_ILOCK_EXCL;
-       xfs_ilock(ip, lockflags);
-
        if ((flags & XFS_QMOPT_INHERIT) && XFS_INHERIT_GID(ip))
                gid = inode->i_gid;
 
@@ -1879,37 +1875,22 @@ xfs_qm_vop_dqalloc(
         * if necessary. The dquot(s) will not be locked.
         */
        if (XFS_NOT_DQATTACHED(mp, ip)) {
+               xfs_ilock(ip, XFS_ILOCK_EXCL);
                error = xfs_qm_dqattach_locked(ip, true);
-               if (error) {
-                       xfs_iunlock(ip, lockflags);
+               xfs_iunlock(ip, XFS_ILOCK_EXCL);
+               if (error)
                        return error;
-               }
        }
 
        if ((flags & XFS_QMOPT_UQUOTA) && XFS_IS_UQUOTA_ON(mp)) {
                ASSERT(O_udqpp);
                if (!uid_eq(inode->i_uid, uid)) {
-                       /*
-                        * What we need is the dquot that has this uid, and
-                        * if we send the inode to dqget, the uid of the inode
-                        * takes priority over what's sent in the uid argument.
-                        * We must unlock inode here before calling dqget if
-                        * we're not sending the inode, because otherwise
-                        * we'll deadlock by doing trans_reserve while
-                        * holding ilock.
-                        */
-                       xfs_iunlock(ip, lockflags);
                        error = xfs_qm_dqget(mp, from_kuid(user_ns, uid),
                                        XFS_DQTYPE_USER, true, &uq);
                        if (error) {
                                ASSERT(error != -ENOENT);
                                return error;
                        }
-                       /*
-                        * Get the ilock in the right order.
-                        */
-                       lockflags = XFS_ILOCK_SHARED;
-                       xfs_ilock(ip, lockflags);
                } else {
                        /*
                         * Take an extra reference, because we'll return
@@ -1922,15 +1903,12 @@ xfs_qm_vop_dqalloc(
        if ((flags & XFS_QMOPT_GQUOTA) && XFS_IS_GQUOTA_ON(mp)) {
                ASSERT(O_gdqpp);
                if (!gid_eq(inode->i_gid, gid)) {
-                       xfs_iunlock(ip, lockflags);
                        error = xfs_qm_dqget(mp, from_kgid(user_ns, gid),
                                        XFS_DQTYPE_GROUP, true, &gq);
                        if (error) {
                                ASSERT(error != -ENOENT);
                                goto error_rele;
                        }
-                       lockflags = XFS_ILOCK_SHARED;
-                       xfs_ilock(ip, lockflags);
                } else {
                        ASSERT(ip->i_gdquot);
                        gq = xfs_qm_dqhold(ip->i_gdquot);
@@ -1939,15 +1917,12 @@ xfs_qm_vop_dqalloc(
        if ((flags & XFS_QMOPT_PQUOTA) && XFS_IS_PQUOTA_ON(mp)) {
                ASSERT(O_pdqpp);
                if (ip->i_projid != prid) {
-                       xfs_iunlock(ip, lockflags);
                        error = xfs_qm_dqget(mp, prid,
                                        XFS_DQTYPE_PROJ, true, &pq);
                        if (error) {
                                ASSERT(error != -ENOENT);
                                goto error_rele;
                        }
-                       lockflags = XFS_ILOCK_SHARED;
-                       xfs_ilock(ip, lockflags);
                } else {
                        ASSERT(ip->i_pdquot);
                        pq = xfs_qm_dqhold(ip->i_pdquot);
@@ -1955,7 +1930,6 @@ xfs_qm_vop_dqalloc(
        }
        trace_xfs_dquot_dqalloc(ip);
 
-       xfs_iunlock(ip, lockflags);
        if (O_udqpp)
                *O_udqpp = uq;
        else