[PATCH V7 16/19] famfs_fuse: Add holder_operations for dax notify_failure()

John Groves
2026-01-18T22:33:42Z

From: John Groves <john@groves.net>

Memory errors are at least somewhat more likely on disaggregated memory
than on-board memory. This commit registers to be notified by fsdev_dax
in the event that a memory failure is detected.

When a file access resolves to a daxdev with memory errors, it will fail
with an appropriate error.

If a daxdev failed fs_dax_get(), we set dd->dax_err. If a daxdev called
our notify_failure(), set dd->error. When any of the above happens, set
(file)->error and stop allowing access.

In general, the recovery from memory errors is to unmount the file
system and re-initialize the memory, but there may be usable degraded
modes of operation - particularly in the future when famfs supports
file systems backed by more than one daxdev. In those cases,
accessing data that is on a working daxdev can still work.

For now, return errors for any file that has encountered a memory or dax
error.

Signed-off-by: John Groves <john@groves.net>
---
fs/fuse/famfs.c | 110 +++++++++++++++++++++++++++++++++++++++---
fs/fuse/famfs_kfmap.h | 3 +-
2 files changed, 105 insertions(+), 8 deletions(-)

diff --git a/fs/fuse/famfs.c b/fs/fuse/famfs.c
index 0218c2a61bc1..b38e92d8f381 100644
--- a/fs/fuse/famfs.c
+++ b/fs/fuse/famfs.c
@@ -21,6 +21,26 @@
#include "famfs_kfmap.h"
#include "fuse_i.h"

+static void famfs_set_daxdev_err(
+ struct fuse_conn *fc, struct dax_device *dax_devp);
+
+static int
+famfs_dax_notify_failure(struct dax_device *dax_devp, u64 offset,
+ u64 len, int mf_flags)
+{
+ struct fuse_conn *fc = dax_holder(dax_devp);
+
+ famfs_set_daxdev_err(fc, dax_devp);
+
+ return 0;
+}
+
+static const struct dax_holder_operations famfs_fuse_dax_holder_ops = {
+ .notify_failure = famfs_dax_notify_failure,
+};
+
+/*****************************************************************************/
+
/*
* famfs_teardown()
*
@@ -47,9 +67,12 @@ famfs_teardown(struct fuse_conn *fc)
if (!dd->valid)
continue;

- /* Release reference from dax_dev_get() */
- if (dd->devp)
+ /* Only call fs_put_dax if fs_dax_get succeeded */
+ if (dd->devp) {
+ if (!dd->dax_err)
+ fs_put_dax(dd->devp, fc);
put_dax(dd->devp);
+ }

kfree(dd->name);
}
@@ -172,6 +195,17 @@ famfs_fuse_get_daxdev(struct fuse_mount *fm, const u64 index)
return -ENODEV;
}

+ rc = fs_dax_get(daxdev->devp, fc, &famfs_fuse_dax_holder_ops);
+ if (rc) {
+ /* Mark as valid with dax_err to prevent retry loop.
+ * famfs_dax_err() will return -EIO on access attempts.
+ * Teardown handles this case: skips fs_put_dax, calls put_dax.
+ */
+ daxdev->dax_err = 1;
+ pr_err("%s: fs_dax_get(%lld) failed\n",
+ __func__, (u64)daxdev->devno);
+ }
+
wmb(); /* All other fields must be visible before valid */
daxdev->valid = 1;
}
@@ -247,6 +281,36 @@ famfs_update_daxdev_table(
return 0;
}

+static void
+famfs_set_daxdev_err(
+ struct fuse_conn *fc,
+ struct dax_device *dax_devp)
+{
+ int i;
+
+ /* Gotta search the list by dax_devp;
+ * read lock because we're not adding or removing daxdev entries
+ */
+ scoped_guard(rwsem_write, &fc->famfs_devlist_sem) {
+ for (i = 0; i < fc->dax_devlist->nslots; i++) {
+ if (fc->dax_devlist->devlist[i].valid) {
+ struct famfs_daxdev *dd;
+
+ dd = &fc->dax_devlist->devlist[i];
+ if (dd->devp != dax_devp)
+ continue;
+
+ dd->error = true;
+
+ pr_err("%s: memory error on daxdev %s (%d)\n",
+ __func__, dd->name, i);
+ return;
+ }
+ }
+ }
+ pr_err("%s: memory err on unrecognized daxdev\n", __func__);
+}
+
/***************************************************************************/

void __famfs_meta_free(void *famfs_meta)
@@ -588,6 +652,26 @@ famfs_file_init_dax(

static int famfs_file_bad(struct inode *inode);

+static int famfs_dax_err(struct famfs_daxdev *dd)
+{
+ if (!dd->valid) {
+ pr_err("%s: daxdev=%s invalid\n",
+ __func__, dd->name);
+ return -EIO;
+ }
+ if (dd->dax_err) {
+ pr_err("%s: daxdev=%s dax_err\n",
+ __func__, dd->name);
+ return -EIO;
+ }
+ if (dd->error) {
+ pr_err("%s: daxdev=%s memory error\n",
+ __func__, dd->name);
+ return -EHWPOISON;
+ }
+ return 0;
+}
+
static int
famfs_interleave_fileofs_to_daxofs(struct inode *inode, struct iomap *iomap,
loff_t file_offset, off_t len, unsigned int flags)
@@ -627,6 +711,7 @@ famfs_interleave_fileofs_to_daxofs(struct inode *inode, struct iomap *iomap,

/* Is the data is in this striped extent? */
if (local_offset < ext_size) {
+ struct famfs_daxdev *dd;
u64 chunk_num = local_offset / chunk_size;
u64 chunk_offset = local_offset % chunk_size;
u64 chunk_remainder = chunk_size - chunk_offset;
@@ -635,6 +720,7 @@ famfs_interleave_fileofs_to_daxofs(struct inode *inode, struct iomap *iomap,
u64 strip_offset = chunk_offset + (stripe_num * chunk_size);
u64 strip_dax_ofs = fei->ie_strips[strip_num].ext_offset;
u64 strip_devidx = fei->ie_strips[strip_num].dev_index;
+ int rc;

if (strip_devidx >= fc->dax_devlist->nslots) {
pr_err("%s: strip_devidx %llu >= nslots %d\n",
@@ -649,6 +735,15 @@ famfs_interleave_fileofs_to_daxofs(struct inode *inode, struct iomap *iomap,
goto err_out;
}

+ dd = &fc->dax_devlist->devlist[strip_devidx];
+
+ rc = famfs_dax_err(dd);
+ if (rc) {
+ /* Shut down access to this file */
+ meta->error = true;
+ return rc;
+ }
+
iomap->addr = strip_dax_ofs + strip_offset;
iomap->offset = file_offset;
iomap->length = min_t(loff_t, len, chunk_remainder);
@@ -746,6 +841,7 @@ famfs_fileofs_to_daxofs(struct inode *inode, struct iomap *iomap,
if (local_offset < dax_ext_len) {
loff_t ext_len_remainder = dax_ext_len - local_offset;
struct famfs_daxdev *dd;
+ int rc;

if (daxdev_idx >= fc->dax_devlist->nslots) {
pr_err("%s: daxdev_idx %llu >= nslots %d\n",
@@ -756,11 +852,11 @@ famfs_fileofs_to_daxofs(struct inode *inode, struct iomap *iomap,

dd = &fc->dax_devlist->devlist[daxdev_idx];

- if (!dd->valid || dd->error) {
- pr_err("%s: daxdev=%lld %s\n", __func__,
- daxdev_idx,
- dd->valid ? "error" : "invalid");
- goto err_out;
+ rc = famfs_dax_err(dd);
+ if (rc) {
+ /* Shut down access to this file */
+ meta->error = true;
+ return rc;
}

/*
diff --git a/fs/fuse/famfs_kfmap.h b/fs/fuse/famfs_kfmap.h
index eb9f70b5cb81..0fff841f5a9e 100644
--- a/fs/fuse/famfs_kfmap.h
+++ b/fs/fuse/famfs_kfmap.h
@@ -73,7 +73,8 @@ struct famfs_file_meta {
struct famfs_daxdev {
/* Include dev uuid? */
bool valid;
- bool error;
+ bool error; /* Dax has reported a memory error (probably poison) */
+ bool dax_err; /* fs_dax_get() failed */
dev_t devno;
struct dax_device *devp;
char *name;
--
2.52.0