linux-kernel - [PATCH v3 2/6] gfs2: Replace kmap_atomic()+memcpy by memcpy_from

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Message-ID: <4d132d7aa9cc71f88e6e02c8f6fcb0fec56542aa.1688073459.git.drv@mailo.com>
Date:   Fri, 30 Jun 2023 03:20:07 +0530
From:   Deepak R Varma <drv@...lo.com>
To:     Bob Peterson <rpeterso@...hat.com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        cluster-devel@...hat.com, linux-kernel@...r.kernel.org
Cc:     Ira Weiny <ira.weiny@...el.com>,
        "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Sumitra Sharma <sumitraartsy@...il.com>,
        Deepak R Varma <drv@...lo.com>
Subject: [PATCH v3 2/6] gfs2: Replace kmap_atomic()+memcpy by
 memcpy_from_page()

kmap_atomic() is deprecated in favor of kmap_local_{folio,page}().

kmap_atomic() disables page-faults and preemption (the latter only for
!PREEMPT_RT kernels), However, the code within the mapping/un-mapping in
gfs2_internal_read() does not depend on the above-mentioned side effects.

Further, memcpy_{from,to}_page() wrappers combine the
{kmap, unmap}_local_page() blocks when they are intended exclusively to
copy contents from/to the temporary mapped page. So, replace the
kmap_atomic()/kunmap_automic() block by the memcpy_from_page() API call.
This change allows to tidy-up code and also eliminate unused variable p.

Suggested-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
Signed-off-by: Deepak R Varma <drv@...lo.com>
---
Changes in v3:
   - Split as a separate patch for conversion in gfs2_internal_read() 
   - Use memcpy_from_page() as suggested by Fabio and  Andreas G
   - Included split version in patch set

Changes in v2:
   - Update patch description to correct the replacement function name
     from kmap_local_folio to kmap_local _page



 fs/gfs2/aops.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/gfs2/aops.c b/fs/gfs2/aops.c
index 3eac4f2f5c27..f47fed657763 100644
--- a/fs/gfs2/aops.c
+++ b/fs/gfs2/aops.c
@@ -489,7 +489,6 @@ int gfs2_internal_read(struct gfs2_inode *ip, char *buf, loff_t *pos,
 	unsigned copied = 0;
 	unsigned amt;
 	struct page *page;
-	void *p;
 
 	do {
 		page = read_cache_page(mapping, index, gfs2_read_folio, NULL);
@@ -498,12 +497,12 @@ int gfs2_internal_read(struct gfs2_inode *ip, char *buf, loff_t *pos,
 				continue;
 			return PTR_ERR(page);
 		}
-		p = kmap_atomic(page);
-		amt = size - copied;
 		if (offset + size > PAGE_SIZE)
 			amt = PAGE_SIZE - offset;
-		memcpy(buf + copied, p + offset, amt);
-		kunmap_atomic(p);
+		else
+			amt = size - copied;
+
+		memcpy_from_page(buf, page, offset, amt);
 		put_page(page);
 		copied += amt;
 		index++;
-- 
2.34.1