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authorDavid Howells <dhowells@redhat.com>2024-01-04 15:52:11 +0000
committerDavid Howells <dhowells@redhat.com>2024-01-05 15:42:25 +0000
commit92a714d727ec9e7ccfcc7432d348aba730145914 (patch)
treea2520df471df8686b9a7d4cab45aff5ba3ba0511 /fs/cachefiles
parent4088e389476e3baababf9b22f34b9d8b3e557344 (diff)
netfs: Fix interaction between write-streaming and cachefiles culling
An issue can occur between write-streaming (storing dirty data in partial non-uptodate pages) and a cachefiles object being culled to make space. The problem occurs because the cache object is only marked in use while there are files open using it. Once it has been released, it can be culled and the cookie marked disabled. At this point, a streaming write is permitted to occur (if the cache is active, we require pages to be prefetched and cached), but the cache can become active again before this gets flushed out - and then two effects can occur: (1) The cache may be asked to write out a region that's less than its DIO block size (assumed by cachefiles to be PAGE_SIZE) - and this causes one of two debugging statements to be emitted. (2) netfs_how_to_modify() gets confused because it sees a page that isn't allowed to be non-uptodate being uptodate and tries to prefetch it - leading to a warning that PG_fscache is set twice. Fix this by the following means: (1) Add a netfs_inode flag to disallow write-streaming to an inode and set it if we ever do local caching of that inode. It remains set for the lifetime of that inode - even if the cookie becomes disabled. (2) If the no-write-streaming flag is set, then make netfs_how_to_modify() always want to prefetch instead. (3) If netfs_how_to_modify() decides it wants to prefetch a folio, but that folio has write-streamed data in it, then it requires the folio be flushed first. (4) Export a counter of the number of times we wanted to prefetch a non-uptodate page, but found it had write-streamed data in it. (5) Export a counter of the number of times we cancelled a write to the cache because it didn't DIO align and remove the debug statements. Reported-by: Marc Dionne <marc.dionne@auristor.com> Signed-off-by: David Howells <dhowells@redhat.com> cc: Jeff Layton <jlayton@kernel.org> cc: linux-cachefs@redhat.com cc: linux-erofs@lists.ozlabs.org cc: linux-fsdevel@vger.kernel.org cc: linux-mm@kvack.org
Diffstat (limited to 'fs/cachefiles')
-rw-r--r--fs/cachefiles/io.c12
1 files changed, 6 insertions, 6 deletions
diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
index 7529b40bc95a..3eec26967437 100644
--- a/fs/cachefiles/io.c
+++ b/fs/cachefiles/io.c
@@ -528,12 +528,12 @@ int __cachefiles_prepare_write(struct cachefiles_object *object,
/* Round to DIO size */
start = round_down(*_start, PAGE_SIZE);
- if (start != *_start) {
- kleave(" = -ENOBUFS [down]");
- return -ENOBUFS;
- }
- if (*_len > upper_len) {
- kleave(" = -ENOBUFS [up]");
+ if (start != *_start || *_len > upper_len) {
+ /* Probably asked to cache a streaming write written into the
+ * pagecache when the cookie was temporarily out of service to
+ * culling.
+ */
+ fscache_count_dio_misfit();
return -ENOBUFS;
}