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    Subject[PATCH 5.18 0017/1095] add barriers to buffer_uptodate and set_buffer_uptodate
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    From: Mikulas Patocka <mpatocka@redhat.com>

    commit d4252071b97d2027d246f6a82cbee4d52f618b47 upstream.

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    include/linux/buffer_head.h | 25 ++++++++++++++++++++++++-
    1 file changed, 24 insertions(+), 1 deletion(-)

    --- a/include/linux/buffer_head.h
    +++ b/include/linux/buffer_head.h
    @@ -117,7 +117,6 @@ static __always_inline int test_clear_bu
    * 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)
    @@ -135,6 +134,30 @@ 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 */

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