bcachefs: Deadlock prevention for ei_pagecache_lock

In the dio write path, when get_user_pages() invokes the fault handler
we have a recursive locking situation - we have to handle the lock
ordering ourselves or we have a deadlock: this patch addresses that by
checking for locking ordering violations and doing the unlock/relock
dance if necessary.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/bcachefs/fs.c b/fs/bcachefs/fs.c
index 3e3ab4e53f33..231a5433577f 100644
--- a/fs/bcachefs/fs.c
+++ b/fs/bcachefs/fs.c
@@ -93,6 +93,11 @@ void bch2_pagecache_add_put(struct pagecache_lock *lock)
 	__pagecache_lock_put(lock, 1);
 }
 
+bool bch2_pagecache_add_tryget(struct pagecache_lock *lock)
+{
+	return __pagecache_lock_tryget(lock, 1);
+}
+
 void bch2_pagecache_add_get(struct pagecache_lock *lock)
 {
 	__pagecache_lock_get(lock, 1);