From f4b554af9931585174d4913b482eacab75858964 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 20 Jul 2015 00:50:55 +0200 Subject: [PATCH] fix the broken lockdep logic in __sb_start_write() 1. wait_event(frozen < level) without rwsem_acquire_read() is just wrong from lockdep perspective. If we are going to deadlock because the caller is buggy, lockdep can't detect this problem. 2. __sb_start_write() can race with thaw_super() + freeze_super(), and after "goto retry" the 2nd acquire_freeze_lock() is wrong. 3. The "tell lockdep we are doing trylock" hack doesn't look nice. I think this is correct, but this logic should be more explicit. Yes, the recursive read_lock() is fine if we hold the lock on a higher level. But we do not need to fool lockdep. If we can not deadlock in this case then try-lock must not fail and we can use use wait == F throughout this code. Note: as Dave Chinner explains, the "trylock" hack and the fat comment can be probably removed. But this needs a separate change and it will be trivial: just kill __sb_start_write() and rename do_sb_start_write() back to __sb_start_write(). Signed-off-by: Oleg Nesterov Reviewed-by: Jan Kara --- Reading git-format-patch failed