[lustre-devel] [PATCH 02/33] Revert "lustre: llite: Check vmpage in releasepage"

[James Simmons <jsimmons@infradead.org>]

From: Patrick Farrell <pfarrell@whamcloud.com>

This reverts commit 9c78efe1a483968c6f84092cb6e59a3f64bc13d6,
because it breaks releasepage for Lustre and does not
completely fix the data consistency issue in LU-14541.

Breaking releasepage matters because it prevents direct I/O
from working if there is page cache data present, and
because it causes similar issues with GDS, which must be
able to flush page cache pages before doing I/O.

With patches:
commit e02cfe39f908 ("lustre: llite: SIGBUS is possible on a race with page reclaim")
and
commit 6af2199c4868 ("lustre: llite: Check for page deletion after fault")
LU-14541 is fully resolved, so we can revert this patch.

WC-bug-id: https://jira.whamcloud.com/browse/LU-14541
Lustre-commit: e3cfb688ed7116a57 ("Revert "lustre: llite: Check vmpage in releasepage")
Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/49654
Reviewed-by: Andrew Perepechko <andrew.perepechko@hpe.com>
Reviewed-by: Qian Yingjin <qian@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
---
 fs/lustre/include/cl_object.h |  9 ---------
 fs/lustre/llite/rw26.c        | 19 ++++++-------------
 fs/lustre/osc/osc_page.c      |  9 ++-------
 3 files changed, 8 insertions(+), 29 deletions(-)

diff --git a/fs/lustre/include/cl_object.h b/fs/lustre/include/cl_object.h
index 77f00d7fc220..94e7f8060d4a 100644
--- a/fs/lustre/include/cl_object.h
+++ b/fs/lustre/include/cl_object.h
@@ -91,7 +91,6 @@
 #include <linux/uio.h>
 #include <lu_object.h>
 #include <linux/atomic.h>
-#include <linux/mm.h>
 #include <linux/mutex.h>
 #include <linux/radix-tree.h>
 #include <linux/spinlock.h>
@@ -989,14 +988,6 @@ static inline bool __page_in_use(const struct cl_page *page, int refc)
  */
 #define cl_page_in_use_noref(pg) __page_in_use(pg, 0)
 
-/* references: cl_page, page cache, optional + refcount for caller reference
- * (always 0 or 1 currently)
- */
-static inline int vmpage_in_use(struct page *vmpage, int refcount)
-{
-	return (page_count(vmpage) - page_mapcount(vmpage) > 2 + refcount);
-}
-
 /** @} cl_page */
 
 /** \addtogroup cl_lock cl_lock
diff --git a/fs/lustre/llite/rw26.c b/fs/lustre/llite/rw26.c
index 6b338b20e7d5..2065e14e8469 100644
--- a/fs/lustre/llite/rw26.c
+++ b/fs/lustre/llite/rw26.c
@@ -109,7 +109,7 @@ static int ll_releasepage(struct page *vmpage, gfp_t gfp_mask)
 {
 	struct lu_env *env;
 	struct cl_object *obj;
-	struct cl_page *clpage;
+	struct cl_page *page;
 	struct address_space *mapping;
 	int result = 0;
 
@@ -125,23 +125,16 @@ static int ll_releasepage(struct page *vmpage, gfp_t gfp_mask)
 	if (!obj)
 		return 1;
 
-	clpage = cl_vmpage_page(vmpage, obj);
-	if (!clpage)
+	page = cl_vmpage_page(vmpage, obj);
+	if (!page)
 		return 1;
 
 	env = cl_env_percpu_get();
 	LASSERT(!IS_ERR(env));
 
-	/* we must not delete the cl_page if the vmpage is in use, otherwise we
-	 * disconnect the vmpage from Lustre while it's still alive(!), which
-	 * means we won't find it to discard on lock cancellation.
-	 *
-	 * References here are: caller + cl_page + page cache.
-	 * Any other references are potentially transient and must be ignored.
-	 */
-	if (!cl_page_in_use(clpage) && !vmpage_in_use(vmpage, 1)) {
+	if (!cl_page_in_use(page)) {
 		result = 1;
-		cl_page_delete(env, clpage);
+		cl_page_delete(env, page);
 	}
 
 	/* To use percpu env array, the call path can not be rescheduled;
@@ -158,7 +151,7 @@ static int ll_releasepage(struct page *vmpage, gfp_t gfp_mask)
 	 * that we won't get into object delete path.
 	 */
 	LASSERT(cl_object_refc(obj) > 1);
-	cl_page_put(env, clpage);
+	cl_page_put(env, page);
 
 	cl_env_percpu_put(env);
 	return result;
diff --git a/fs/lustre/osc/osc_page.c b/fs/lustre/osc/osc_page.c
index feec99fe0ca2..f700b5af7de0 100644
--- a/fs/lustre/osc/osc_page.c
+++ b/fs/lustre/osc/osc_page.c
@@ -520,13 +520,8 @@ static inline bool lru_page_busy(struct client_obd *cli, struct cl_page *page)
 	if (cli->cl_cache->ccc_unstable_check) {
 		struct page *vmpage = cl_page_vmpage(page);
 
-		/* this check is racy because the vmpage is not locked, but
-		 * that's OK - the code which does the actual page release
-		 * checks this again before releasing
-		 *
-		 * vmpage have two known users: cl_page and VM page cache
-		 */
-		if (vmpage_in_use(vmpage, 0))
+		/* vmpage have two known users: cl_page and VM page cache */
+		if (page_count(vmpage) - page_mapcount(vmpage) > 2)
 			return true;
 	}
 	return false;
-- 
2.39.3

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