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fuse: back uncached readdir buffers with pages

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Commit dabb903910 ("fuse: increase readdir buffer size") changed
fuse_readdir_uncached() to size its temporary buffer from ctx->count.
This is useful for overlayfs and other in-kernel callers that use
INT_MAX to indicate an unlimited directory read.

The larger buffer is currently supplied as a kvec output argument. For
virtiofs, kvec arguments are copied through req->argbuf, which is
allocated with kmalloc(..., GFP_ATOMIC). A large uncached readdir buffer
can therefore require a multi-megabyte contiguous atomic allocation
before the request is queued.

Avoid the large bounce-buffer allocation by backing uncached readdir
output with pages and setting out_pages. Transports such as virtiofs can
then pass the pages as scatter-gather entries instead of copying the
output through argbuf.

Map the pages with vm_map_ram() only while parsing the returned dirents.
The existing parser can then continue to use a linear kernel mapping.

[SzM: separate allocation of pages into a helper function]

Fixes: dabb903910 ("fuse: increase readdir buffer size")
Cc: stable@vger.kernel.org
Signed-off-by: Matthew R. Ochs <mochs@nvidia.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Matthew R. Ochs 2026-05-26 08:20:21 -07:00 committed by Miklos Szeredi
parent 06b4135177
commit 4dd6f6d308
1 changed files with 67 additions and 18 deletions
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85
fs/fuse/readdir.c
View File

@ -12,6 +12,7 @@
#include <linux/posix_acl.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/vmalloc.h>
static bool fuse_use_readdirplus(struct inode *dir, struct dir_context *ctx)
{
@ -335,6 +336,43 @@ static int parse_dirplusfile(char *buf, size_t nbytes, struct file *file,
return 0;
}
static struct page **fuse_readdir_alloc_buf(struct fuse_args_pages *ap, size_t *bufsize)
{
unsigned int i, nr_alloc, nr_pages = DIV_ROUND_UP(*bufsize, PAGE_SIZE);
struct page **pages = kcalloc(nr_pages, sizeof(*pages), GFP_KERNEL);
if (!pages)
return NULL;
nr_alloc = alloc_pages_bulk(GFP_KERNEL, nr_pages, pages);
if (!nr_alloc)
goto free_array;
if (nr_alloc < nr_pages) {
nr_pages = nr_alloc;
*bufsize = (size_t) nr_pages << PAGE_SHIFT;
}
ap->folios = fuse_folios_alloc(nr_pages, GFP_KERNEL, &ap->descs);
if (!ap->folios)
goto release_pages;
for (i = 0; i < nr_pages; i++) {
ap->folios[i] = page_folio(pages[i]);
ap->descs[i].length = min_t(size_t, *bufsize - (size_t)i * PAGE_SIZE, PAGE_SIZE);
}
ap->num_folios = nr_pages;
ap->args.out_pages = true;
return pages;
release_pages:
release_pages(pages, nr_pages);
free_array:
kfree(pages);
return NULL;
}
static int fuse_readdir_uncached(struct file *file, struct dir_context *ctx)
{
int plus;
@ -343,18 +381,16 @@ static int fuse_readdir_uncached(struct file *file, struct dir_context *ctx)
struct fuse_mount *fm = get_fuse_mount(inode);
struct fuse_conn *fc = fm->fc;
struct fuse_io_args ia = {};
struct fuse_args *args = &ia.ap.args;
struct fuse_args_pages *ap = &ia.ap;
void *buf;
size_t bufsize = clamp((unsigned int) ctx->count, PAGE_SIZE, fc->max_pages << PAGE_SHIFT);
u64 attr_version = 0, evict_ctr = 0;
bool locked;
struct page **pages = fuse_readdir_alloc_buf(ap, &bufsize);
buf = kvmalloc(bufsize, GFP_KERNEL);
if (!buf)
if (!pages)
return -ENOMEM;
args->out_args[0].value = buf;
plus = fuse_use_readdirplus(inode, ctx);
if (plus) {
attr_version = fuse_get_attr_version(fm->fc);
@ -364,24 +400,37 @@ static int fuse_readdir_uncached(struct file *file, struct dir_context *ctx)
fuse_read_args_fill(&ia, file, ctx->pos, bufsize, FUSE_READDIR);
}
locked = fuse_lock_inode(inode);
res = fuse_simple_request(fm, args);
res = fuse_simple_request(fm, &ap->args);
fuse_unlock_inode(inode, locked);
if (res >= 0) {
if (!res) {
struct fuse_file *ff = file->private_data;
if (res < 0)
goto out;
if (ff->open_flags & FOPEN_CACHE_DIR)
fuse_readdir_cache_end(file, ctx->pos);
} else if (plus) {
res = parse_dirplusfile(buf, res, file, ctx, attr_version,
evict_ctr);
} else {
res = parse_dirfile(buf, res, file, ctx);
}
if (!res) {
struct fuse_file *ff = file->private_data;
if (ff->open_flags & FOPEN_CACHE_DIR)
fuse_readdir_cache_end(file, ctx->pos);
goto out;
}
kvfree(buf);
buf = vm_map_ram(pages, ap->num_folios, -1);
if (!buf) {
res = -ENOMEM;
} else {
if (plus)
res = parse_dirplusfile(buf, res, file, ctx, attr_version, evict_ctr);
else
res = parse_dirfile(buf, res, file, ctx);
vm_unmap_ram(buf, ap->num_folios);
}
out:
kfree(ap->folios);
release_pages(pages, ap->num_folios);
kfree(pages);
fuse_invalidate_atime(inode);
return res;
}