From: geruijun geruijun@huawei.com
euleros inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I4M0EE?from=project-issue
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We found the following deadlock when running xfstests generic/390 with ext4 filesystem, and simutaneously offlining/onlining the disk we tested. It will cause a deadlock whose call trace is like this:
fsstress D 0 11672 11625 0x00000080 Call Trace: ? __schedule+0x2fc/0x930 ? filename_parentat+0x10b/0x1a0 schedule+0x28/0x70 rwsem_down_read_failed+0x102/0x1c0 ? __percpu_down_read+0x93/0xb0 __percpu_down_read+0x93/0xb0 __sb_start_write+0x5f/0x70 mnt_want_write+0x20/0x50 do_renameat2+0x1f3/0x550 __x64_sys_rename+0x1c/0x20 do_syscall_64+0x5b/0x1b0 entry_SYSCALL_64_after_hwframe+0x65/0xca
The root cause is that when ext4 hits IO error due to disk being offline, it will switch itself into read-only state. When it is frozen at that moment, following thaw_super() call will not unlock percpu freeze semaphores (as the fs is read-only) causing the deadlock.
Fix the problem by tracking whether the superblock was read-only at the time we were freezing it.
Reported-and-tested-by: Shijie Luo luoshijie1@huawei.com Signed-off-by: geruijun geruijun@huawei.com Signed-off-by: Jan Kara jack@suse.cz Reviewed-by: Zhang Yi yi.zhang@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- fs/super.c | 9 ++++++++- include/linux/fs.h | 4 +++- 2 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/fs/super.c b/fs/super.c index 98bb0629ee10..494bfdc6f778 100644 --- a/fs/super.c +++ b/fs/super.c @@ -1727,10 +1727,12 @@ int freeze_super(struct super_block *sb) if (sb_rdonly(sb)) { /* Nothing to do really... */ sb->s_writers.frozen = SB_FREEZE_COMPLETE; + sb->s_writers.frozen_ro = 1; up_write(&sb->s_umount); return 0; }
+ sb->s_writers.frozen_ro = 0; sb->s_writers.frozen = SB_FREEZE_WRITE; /* Release s_umount to preserve sb_start_write -> s_umount ordering */ up_write(&sb->s_umount); @@ -1786,7 +1788,12 @@ static int thaw_super_locked(struct super_block *sb) return -EINVAL; }
- if (sb_rdonly(sb)) { + /* + * Was the fs frozen in read-only state? Note that we cannot just check + * sb_rdonly(sb) as the filesystem might have switched to read-only + * state due to internal errors or so. + */ + if (sb->s_writers.frozen_ro) { sb->s_writers.frozen = SB_UNFROZEN; goto out; } diff --git a/include/linux/fs.h b/include/linux/fs.h index 243a0987ca2b..a56184847086 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1413,7 +1413,9 @@ enum { #define SB_FREEZE_LEVELS (SB_FREEZE_COMPLETE - 1)
struct sb_writers { - int frozen; /* Is sb frozen? */ + unsigned short frozen; /* Is sb frozen? */ + unsigned short frozen_ro; /* Was sb read-only + * when frozen? */ wait_queue_head_t wait_unfrozen; /* for get_super_thawed() */ struct percpu_rw_semaphore rw_sem[SB_FREEZE_LEVELS]; };