fs: allow all writers to be frozen

During freeze/thaw we need to be able to freeze all writers during
suspend/hibernate. Otherwise tasks such as systemd-journald that mmap a
file and write to it will not be frozen after we've already frozen the
filesystem.

This has some risk of not being able to freeze processes in case a
process has acquired SB_FREEZE_PAGEFAULT under mmap_sem or
SB_FREEZE_INTERNAL under some other filesytem specific lock. If the
filesystem is frozen, a task can block on the frozen filesystem with
e.g., mmap_sem held. If some other task then blocks on grabbing that
mmap_sem, hibernation ill fail because it is unable to hibernate a task
holding mmap_sem. This could be fixed by making a range of filesystem
related locks use freezable sleeping. That's impractical and not
warranted just for suspend/hibernate. Assume that this is an infrequent
problem and we've given userspace a way to skip filesystem freezing
through a sysfs file.

Link: https://lore.kernel.org/r/20250402-work-freeze-v2-2-6719a97b52ac@kernel.org
Link: https://lore.kernel.org/r/20250327140613.25178-3-James.Bottomley@HansenPartnership.com
[brauner: make all freeze levels set TASK_FREEZABLE and rewrite commit message]
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 016b0fe1536e3630eccb10df3f6f93393c97966b..35b81f4979048a3bcb70f52c2a2dfaaf2a75891a 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1780,7 +1780,7 @@ 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, true);
 }
 
 static inline bool __sb_start_write_trylock(struct super_block *sb, int level)