fs: fix a hungtask problem when freeze/unfreeze fs

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>