On Thu, Oct 31, 2019 at 05:32:55PM +0200, Alex Lyakas wrote: > From: Vratislav Bendel <vbendel@xxxxxxxxxx> > > [upstream commit 19957a181608d25c8f4136652d0ea00b3738972d] > > Due to an inverted logic mistake in xfs_buftarg_isolate() > the xfs_buffers with zero b_lru_ref will take another trip > around LRU, while isolating buffers with non-zero b_lru_ref. > > Additionally those isolated buffers end up right back on the LRU > once they are released, because b_lru_ref remains elevated. > > Fix that circuitous route by leaving them on the LRU > as originally intended. > > [Additional description for the issue] > > Due to this issue, buffers will spend one cycle less in > the LRU than intended. If we initialize b_lru_ref to X, we intend the > buffer to survive X shrinker calls, and on the X+1'th call to be taken > off the LRU (and maybe freed). But with this issue, the buffer will be > taken off the LRU and immediately re-added back. But this will happen > X-1 times, because on the X'th time the b_lru_ref will be 0, and the > buffer will not be re-added to the LRU. So the buffer will survive X-1 > shrinker calls and not X as intended. > > Furthermore, if somehow we end up with the buffer sitting on the LRU > and having b_lru_ref==0, this buffer will never be taken off the LRU, > due to the bug. Not sure that this can happen, because by default > b_lru_ref is set to 1. > > This issue existed since the introduction of lru in XFS buffer cache > in commit > "430cbeb86fdcbbdabea7d4aa65307de8de425350 xfs: add a lru to the XFS buffer cache". > > However, the integration with the "list_lru" insfrastructure was done in kernel 3.12, > in commit > "e80dfa19976b884db1ac2bc5d7d6ca0a4027bd1c xfs: convert buftarg LRU to generic code" > > Therefore this patch is relevant for all kernels from 3.12 to 4.15 > (upstream fix was made in 4.16). > > Signed-off-by: Alex Lyakas <alex@xxxxxxxxxx> > Signed-off-by: Vratislav Bendel <vbendel@xxxxxxxxxx> > Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx> > Reviewed-by: Christoph Hellwig <hch@xxxxxx> > Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > (cherry picked from commit 19957a181608d25c8f4136652d0ea00b3738972d) > --- > fs/xfs/xfs_buf.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Now queued up, thanks. greg k-h
