[RFC PATCH 2/4] vfs: make sb_start_write freezable

[James Bottomley <James.Bottomley@HansenPartnership.com>]

If a write happens on a frozen filesystem, the s_writers.rw_sem gets
stuck in TASK_UNINTERRUPTIBLE and inhibits suspending or hibernating
the system.  Since we want to freeze filesystems first then tasks, we
need this condition not to inhibit suspend/hibernate, which means the
wait has to have the TASK_FREEZABLE flag as well.  Use the freezable
version of percpu-rwsem to ensure this.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
---
 include/linux/fs.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index dd84d1c3b8af..cbbb704eff74 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1782,7 +1782,8 @@ static inline void __sb_end_write(struct super_block *sb, int level)
 
 static inline void __sb_start_write(struct super_block *sb, int level)
 {
-	percpu_down_read(sb->s_writers.rw_sem + level - 1);
+	percpu_down_read_freezable(sb->s_writers.rw_sem + level - 1,
+				   level == SB_FREEZE_WRITE);
 }
 
 static inline bool __sb_start_write_trylock(struct super_block *sb, int level)
-- 
2.43.0