exfat: make valid_size and zeroed_size atomic

ei->valid_size and ei->zeroed_size are 64-bit fields read from bio
completion context (exfat_iomap_read_end_io()) and from ->iomap_begin
without i_rwsem, while writers update them under i_rwsem.  On 32-bit
these loads can tear, and the "if (x < new) x = new" read-modify-write
can lose an update or regress the value when two writers race.

Convert both to atomic64_t and funnel updates through a cmpxchg-based
monotonic advance helper so the value only moves forward; plain reads use
exfat_get_*(), and the few shrink/init paths (truncate, inode fill,
create) use exfat_set_*().  This is a prerequisite for taking
exfat_page_mkwrite() out from under i_rwsem.

Fixes: 82a81a7352bc ("exfat: add iomap buffered I/O support")
Cc: stable@vger.kernel.org
Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

0 files changed, 0 insertions, 0 deletions