netfs: Fix read abandonment during retry

Under certain circumstances, all the remaining subrequests from a read
request will get abandoned during retry.  The abandonment process expects
the 'subreq' variable to be set to the place to start abandonment from, but
it doesn't always have a useful value (it will be uninitialised on the
first pass through the loop and it may point to a deleted subrequest on
later passes).

Fix the first jump to "abandon:" to set subreq to the start of the first
subrequest expected to need retry (which, in this abandonment case, turned
out unexpectedly to no longer have NEED_RETRY set).

Also clear the subreq pointer after discarding superfluous retryable
subrequests to cause an oops if we do try to access it.

Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/3775287.1773848338@warthog.procyon.org.uk
Reviewed-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
cc: Paulo Alcantara <pc@manguebit.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/netfs/read_retry.c b/fs/netfs/read_retry.c
index 7793ba5e3e8fc1d9862c272844597bcf88646d5d..cca9ac43c07738c2b6069fe6e6096efb69cd9b23 100644 (file)
--- a/fs/netfs/read_retry.c
+++ b/fs/netfs/read_retry.c
@@ -93,8 +93,10 @@ static void netfs_retry_read_subrequests(struct netfs_io_request *rreq)
                       from->start, from->transferred, from->len);
 
                if (test_bit(NETFS_SREQ_FAILED, &from->flags) ||
-                   !test_bit(NETFS_SREQ_NEED_RETRY, &from->flags))
+                   !test_bit(NETFS_SREQ_NEED_RETRY, &from->flags)) {
+                       subreq = from;
                        goto abandon;
+               }
 
                list_for_each_continue(next, &stream->subrequests) {
                        subreq = list_entry(next, struct netfs_io_subrequest, rreq_link);
@@ -178,6 +180,7 @@ static void netfs_retry_read_subrequests(struct netfs_io_request *rreq)
                                if (subreq == to)
                                        break;
                        }
+                       subreq = NULL;
                        continue;
                }