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SubjectRe: [GIT PULL] fscache: I/O API modernisation and netfs helper library
Date
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> Does the code not hold a refcount already?

The attached patch will do that. Note that it's currently based on top of the
patch that drops the PG_fscache alias, so it refers to PG_private_2.

I've run all three patches through xfstests over afs, both with and without a
cache, and Jeff has tested ceph with them.

David
---
commit 803a09110b41b9f6091a517fc8f5c4b15475048c
Author: David Howells <dhowells@redhat.com>
Date: Wed Feb 10 11:35:15 2021 +0000

netfs: Hold a ref on a page when PG_private_2 is set

Take a reference on a page when PG_private_2 is set and drop it once the
bit is unlocked.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: David Howells <dhowells@redhat.com>

diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index 9018224693e9..043d96ca2aad 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -10,6 +10,7 @@
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
+#include <linux/pagevec.h>
#include <linux/slab.h>
#include <linux/uio.h>
#include <linux/sched/mm.h>
@@ -230,10 +231,13 @@ static void netfs_rreq_completed(struct netfs_read_request *rreq)
static void netfs_rreq_unmark_after_write(struct netfs_read_request *rreq)
{
struct netfs_read_subrequest *subreq;
+ struct pagevec pvec;
struct page *page;
pgoff_t unlocked = 0;
bool have_unlocked = false;

+ pagevec_init(&pvec);
+
rcu_read_lock();

list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
@@ -247,6 +251,8 @@ static void netfs_rreq_unmark_after_write(struct netfs_read_request *rreq)
continue;
unlocked = page->index;
unlock_page_private_2(page);
+ if (pagevec_add(&pvec, page) == 0)
+ pagevec_release(&pvec);
have_unlocked = true;
}
}
@@ -403,8 +409,10 @@ static void netfs_rreq_unlock(struct netfs_read_request *rreq)
pg_failed = true;
break;
}
- if (test_bit(NETFS_SREQ_WRITE_TO_CACHE, &subreq->flags))
+ if (test_bit(NETFS_SREQ_WRITE_TO_CACHE, &subreq->flags)) {
+ get_page(page);
SetPagePrivate2(page);
+ }
pg_failed |= subreq_failed;
if (pgend < iopos + subreq->len)
break;
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