git: 70dc6b2ce314 - main - nfsclient: limit situations when we do unlocked read-ahead by nfsiod

The branch main has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=70dc6b2ce314a0f32755005ad02802fca7ed186e

commit 70dc6b2ce314a0f32755005ad02802fca7ed186e
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2024-01-01 22:22:44 +0000
Commit:     Konstantin Belousov <kib@FreeBSD.org>
CommitDate: 2024-01-05 04:58:58 +0000

    nfsclient: limit situations when we do unlocked read-ahead by nfsiod
    
    If there were or are writeable mappings, read-ahead might overwrite the
    dirty pages data that is not yet reflected as a delayed write in the
    matching buffer state.
    
    Noted by:       rmacklem
    Tested by:      pho
    Sponsored by:   The FreeBSD Foundation
    MFC after:      1 week
---
 sys/fs/nfsclient/nfs_clbio.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/sys/fs/nfsclient/nfs_clbio.c b/sys/fs/nfsclient/nfs_clbio.c
index e6486af55daf..f6506e34ee59 100644
--- a/sys/fs/nfsclient/nfs_clbio.c
+++ b/sys/fs/nfsclient/nfs_clbio.c
@@ -481,9 +481,14 @@ ncl_bioread(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred)
 		on = uio->uio_offset - (lbn * biosize);
 
 		/*
-		 * Start the read ahead(s), as required.
+		 * Start the read ahead(s), as required.  Do not do
+		 * read-ahead if there are writeable mappings, since
+		 * unlocked read by nfsiod could obliterate changes
+		 * done by userspace.
 		 */
-		if (nmp->nm_readahead > 0) {
+		if (nmp->nm_readahead > 0 &&
+		    !vm_object_mightbedirty(vp->v_object) &&
+		    vp->v_object->un_pager.vnp.writemappings == 0) {
 		    for (nra = 0; nra < nmp->nm_readahead && nra < seqcount &&
 			(off_t)(lbn + 1 + nra) * biosize < nsize; nra++) {
 			rabn = lbn + 1 + nra;
@@ -671,6 +676,8 @@ ncl_bioread(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred)
 		 */
 		NFSLOCKNODE(np);
 		if (nmp->nm_readahead > 0 &&
+		    !vm_object_mightbedirty(vp->v_object) &&
+		    vp->v_object->un_pager.vnp.writemappings == 0 &&
 		    (bp->b_flags & B_INVAL) == 0 &&
 		    (np->n_direofoffset == 0 ||
 		    (lbn + 1) * NFS_DIRBLKSIZ < np->n_direofoffset) &&