[PATCH 04/14] iomap: move the PF_MEMALLOC check to iomap_writepages

Christoph Hellwig
2023-12-07T07:27:33Z

The iomap writepage implementation has been removed in commit
478af190cb6c ("iomap: remove iomap_writepage") and this code is now only
called through ->writepages which never happens from memory reclaim.

Nove the check from iomap_do_writepage to iomap_writepages so that is
only called once per ->writepage invocation.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/iomap/buffered-io.c | 24 ++++++++----------------
1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index dc5039cdacd928..ef99418f5a7a73 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1912,20 +1912,6 @@ static int iomap_do_writepage(struct folio *folio,

trace_iomap_writepage(inode, folio_pos(folio), folio_size(folio));

- /*
- * Refuse to write the folio out if we're called from reclaim context.
- *
- * This avoids stack overflows when called from deeply used stacks in
- * random callers for direct reclaim or memcg reclaim. We explicitly
- * allow reclaim from kswapd as the stack usage there is relatively low.
- *
- * This should never happen except in the case of a VM regression so
- * warn about it.
- */
- if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
- PF_MEMALLOC))
- goto redirty;
-
/*
* Is this folio beyond the end of the file?
*
@@ -1991,8 +1977,6 @@ static int iomap_do_writepage(struct folio *folio,

return iomap_writepage_map(wpc, wbc, inode, folio, end_pos);

-redirty:
- folio_redirty_for_writepage(wbc, folio);
unlock:
folio_unlock(folio);
return 0;
@@ -2005,6 +1989,14 @@ iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
{
int ret;

+ /*
+ * Writeback from reclaim context should never happen except in the case
+ * of a VM regression so warn about it and refuse to write the data.
+ */
+ if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC | PF_KSWAPD)) ==
+ PF_MEMALLOC))
+ return -EIO;
+
wpc->ops = ops;
ret = write_cache_pages(mapping, wbc, iomap_do_writepage, wpc);
if (!wpc->ioend)
--
2.39.2