From f73bae83675b860cae9f58dba233b6be92e750ca Mon Sep 17 00:00:00 2001 From: James Bottomley Date: Thu, 27 Mar 2025 10:06:11 -0400 Subject: [PATCH] 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 Signed-off-by: James Bottomley Signed-off-by: Christian Brauner --- include/linux/fs.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index 016b0fe1536e..35b81f497904 100644 --- 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) -- 2.25.1