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add barriers to buffer_uptodate and set_buffer_uptodate 

Let's have a look at this piece of code in __bread_slow:

	get_bh(bh);
	bh->b_end_io = end_buffer_read_sync;
	submit_bh(REQ_OP_READ, 0, bh);
	wait_on_buffer(bh);
	if (buffer_uptodate(bh))
		return bh;

Neither wait_on_buffer nor buffer_uptodate contain any memory barrier.
Consequently, if someone calls sb_bread and then reads the buffer data,
the read of buffer data may be executed before wait_on_buffer(bh) on
architectures with weak memory ordering and it may return invalid data.

Fix this bug by adding a memory barrier to set_buffer_uptodate and an
acquire barrier to buffer_uptodate (in a similar way as
folio_test_uptodate and folio_mark_uptodate).

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mikulas Patocka 2022-08-09 14:32:13 -04:00 committed by Linus Torvalds
parent e394ff83bb
commit d4252071b9
1 changed files with 24 additions and 1 deletions
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25
include/linux/buffer_head.h
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@ -118,7 +118,6 @@ static __always_inline int test_clear_buffer_##name(struct buffer_head *bh) \
* of the form "mark_buffer_foo()". These are higher-level functions which
* do something in addition to setting a b_state bit.
*/
BUFFER_FNS(Uptodate, uptodate)
BUFFER_FNS(Dirty, dirty)
TAS_BUFFER_FNS(Dirty, dirty)
BUFFER_FNS(Lock, locked)
@ -136,6 +135,30 @@ BUFFER_FNS(Meta, meta)
BUFFER_FNS(Prio, prio)
BUFFER_FNS(Defer_Completion, defer_completion)
static __always_inline void set_buffer_uptodate(struct buffer_head *bh)
{
/*
* make it consistent with folio_mark_uptodate
* pairs with smp_load_acquire in buffer_uptodate
*/
smp_mb__before_atomic();
set_bit(BH_Uptodate, &bh->b_state);
}
static __always_inline void clear_buffer_uptodate(struct buffer_head *bh)
{
clear_bit(BH_Uptodate, &bh->b_state);
}
static __always_inline int buffer_uptodate(const struct buffer_head *bh)
{
/*
* make it consistent with folio_test_uptodate
* pairs with smp_mb__before_atomic in set_buffer_uptodate
*/
return (smp_load_acquire(&bh->b_state) & (1UL << BH_Uptodate)) != 0;
}
#define bh_offset(bh) ((unsigned long)(bh)->b_data & ~PAGE_MASK)
/* If we *know* page->private refers to buffer_heads */