From 2f007ba074ad77e70d941e16956d1937dc3080c6 Mon Sep 17 00:00:00 2001 From: Mike Snitzer Date: Mon, 28 Sep 2026 11:54:29 -0400 Subject: [PATCH] pNFS/flexfiles: don't read through MDS when previous layout forbid it ff_layout_pg_init_read() falls back to the MDS whenever pnfs_update_layout() returns no segment and no error: a bulk CB_LAYOUTRECALL (FSID, DEVICEID or ALL), LAYOUTGETs blocked behind a layout being returned, or a LAYOUTGET refused with NFS4ERR_LAYOUTUNAVAILABLE or NFS4ERR_TOOSMALL, which set the per-iomode fail bit for PNFS_LAYOUTGET_RETRY_TIMEOUT. That is the read-side twin of the write path fixed by commit 1d62e659c0bf ("NFSv4/flexfiles: honor FF_FLAGS_NO_IO_THRU_MDS in pg_get_mirror_count_write"), and it is reached in exactly the situation that matters most: the file had a valid layout, the layout had to go back, and the next one has not arrived yet. The write side could answer -EAGAIN because writeback owns the retry and redirties the page. A read has no such owner, so -EAGAIN here would surface as an I/O error to the application. Wait for a layout instead, on the same terms the function already uses when the layout lookup itself returns -EAGAIN: sleep a second and retry, bounded by pg_maxretrans, which ff_layout_pg_init_read() sets only for soft and softerr mounts. A hard mount therefore waits, which is what a hard mount is for, and matches what the FF_FLAGS_NO_IO_THRU_MDS check on the data server selection a few lines above already does. That includes waiting out NFS4ERR_LAYOUTUNAVAILABLE: a file that was given a layout with this flag must not be read off the MDS, whatever the server says afterwards. The test asks the inode (NFS_INO_NO_IO_THRU_MDS) rather than the layout hdr, because in this path there is no segment, and the hdr that carried the flag may already have been destroyed. Where a segment is in hand - the data server selection above, ff_layout_read_pagelist() - the existing per-segment ff_layout_no_fallback_to_mds() test stays, since it is the more precise question. Fixes: 260074cd8413 ("pNFS/flexfiles: Add support for FF_FLAGS_NO_IO_THRU_MDS") Assisted-by: Claude:claude-opus-5[1m] Signed-off-by: Mike Snitzer Signed-off-by: Anna Schumaker --- fs/nfs/flexfilelayout/flexfilelayout.c | 38 ++++++++++++++++++-------- 1 file changed, 26 insertions(+), 12 deletions(-) diff --git a/fs/nfs/flexfilelayout/flexfilelayout.c b/fs/nfs/flexfilelayout/flexfilelayout.c index 7d45401ee5b1..84d22f715653 100644 --- a/fs/nfs/flexfilelayout/flexfilelayout.c +++ b/fs/nfs/flexfilelayout/flexfilelayout.c @@ -1073,19 +1073,33 @@ ff_layout_pg_init_read(struct nfs_pageio_descriptor *pgio, if (pgio->pg_error < 0) { if (pgio->pg_error != -EAGAIN) return; - /* Retry getting layout segment if lower layer returned -EAGAIN */ - if (pgio->pg_maxretrans && req->wb_nio++ > pgio->pg_maxretrans) { - if (NFS_SERVER(pgio->pg_inode)->flags & NFS_MOUNT_SOFTERR) - pgio->pg_error = -ETIMEDOUT; - else - pgio->pg_error = -EIO; - return; - } - pgio->pg_error = 0; - /* Sleep for 1 second before retrying */ - ssleep(1); - goto retry; + goto retry_nolseg; } + /* + * No segment, and no error to report either: pnfs_update_layout() + * simply has nothing to give (NFS_LAYOUT_BULK_RECALL, a failed + * pnfs_layout_io_test, blocked LAYOUTGETs, a layout being + * returned). If the server forbids reading this file through the + * MDS there is no fallback to take, so wait for a layout on the + * same terms as the -EAGAIN above. The layout hdr that carried + * FF_FLAGS_NO_IO_THRU_MDS may itself be gone by now, which is why + * this asks the inode and not the hdr. + */ + if (!nfs_no_io_thru_mds(pgio->pg_inode)) + goto out_mds; +retry_nolseg: + /* Retry getting layout segment if lower layer returned -EAGAIN */ + if (pgio->pg_maxretrans && req->wb_nio++ > pgio->pg_maxretrans) { + if (NFS_SERVER(pgio->pg_inode)->flags & NFS_MOUNT_SOFTERR) + pgio->pg_error = -ETIMEDOUT; + else + pgio->pg_error = -EIO; + return; + } + pgio->pg_error = 0; + /* Sleep for 1 second before retrying */ + ssleep(1); + goto retry; out_mds: trace_pnfs_mds_fallback_pg_init_read(pgio->pg_inode, 0, NFS4_MAX_UINT64, IOMODE_READ,