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nfsclient: limit situations when we do unlocked read-ahead by nfsiod

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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
This commit is contained in:
Konstantin Belousov 2024-01-02 00:22:44 +02:00
parent 2d33ad48bd
commit 70dc6b2ce3
1 changed files with 9 additions and 2 deletions
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11
sys/fs/nfsclient/nfs_clbio.c
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@ -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) &&