[PATCH] devpts: fix pty count limit off by one

[Yichong Chen <chenyichong@uniontech.com>]

devpts_new_index() increments the global pty count before checking it
against the effective global limit. The check currently rejects a new pty
when the incremented count is equal to the limit.

This makes kernel.pty.max allow only max - 1 ptys. For example, if
kernel.pty.nr is 3 and kernel.pty.max is set to 4, opening /dev/ptmx
fails with -ENOSPC even though one more pty should be allowed.

Allow the incremented count to be equal to the effective limit and reject
only counts above it.

Fixes: 0f0a0e54a2a1 ("devpts: Convert to new IDA API")
Signed-off-by: Yichong Chen <chenyichong@uniontech.com>
---
 fs/devpts/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 9844dcf354ee..853cc4c03e73 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -467,7 +467,7 @@ int devpts_new_index(struct pts_fs_info *fsi)
 {
 	int index = -ENOSPC;
 
-	if (atomic_inc_return(&pty_count) >= (pty_limit -
+	if (atomic_inc_return(&pty_count) > (pty_limit -
 			  (fsi->mount_opts.reserve ? 0 : pty_reserve)))
 		goto out;
 
-- 
2.51.0