This is a note to let you know that I've just added the patch titled add barriers to buffer_uptodate and set_buffer_uptodate to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: add-barriers-to-buffer_uptodate-and-set_buffer_uptodate.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From d4252071b97d2027d246f6a82cbee4d52f618b47 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka <mpatocka@xxxxxxxxxx> Date: Tue, 9 Aug 2022 14:32:13 -0400 Subject: add barriers to buffer_uptodate and set_buffer_uptodate From: Mikulas Patocka <mpatocka@xxxxxxxxxx> 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@xxxxxxxxxx> Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 */ Patches currently in stable-queue which might be from mpatocka@xxxxxxxxxx are queue-4.19/add-barriers-to-buffer_uptodate-and-set_buffer_uptodate.patch