The patch below does not apply to the 5.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7e7986f9d3ba69a7375a41080a1f8c8012cb0923 Mon Sep 17 00:00:00 2001

From: Mike Snitzer snitzer@redhat.com Date: Tue, 1 Dec 2020 11:07:09 -0500 Subject: [PATCH] block: use gcd() to fix chunk_sectors limit stacking

commit 22ada802ede8 ("block: use lcm_not_zero() when stacking chunk_sectors") broke chunk_sectors limit stacking. chunk_sectors must reflect the most limited of all devices in the IO stack.

Otherwise malformed IO may result. E.g.: prior to this fix, ->chunk_sectors = lcm_not_zero(8, 128) would result in blk_max_size_offset() splitting IO at 128 sectors rather than the required more restrictive 8 sectors.

And since commit 07d098e6bbad ("block: allow 'chunk_sectors' to be non-power-of-2") care must be taken to properly stack chunk_sectors to be compatible with the possibility that a non-power-of-2 chunk_sectors may be stacked. This is why gcd() is used instead of reverting back to using min_not_zero().

Fixes: 22ada802ede8 ("block: use lcm_not_zero() when stacking chunk_sectors") Fixes: 07d098e6bbad ("block: allow 'chunk_sectors' to be non-power-of-2") Reported-by: John Dorminy jdorminy@redhat.com Reported-by: Bruce Johnston bjohnsto@redhat.com Signed-off-by: Mike Snitzer snitzer@redhat.com Reviewed-by: John Dorminy jdorminy@redhat.com Cc: stable@vger.kernel.org Reviewed-by: Martin K. Petersen martin.petersen@oracle.com Signed-off-by: Jens Axboe axboe@kernel.dk

diff --git a/block/blk-settings.c b/block/blk-settings.c index 9741d1d83e98..659cdb8a07fe 100644 --- a/block/blk-settings.c +++ b/block/blk-settings.c @@ -547,7 +547,10 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,

t->io_min = max(t->io_min, b->io_min); t->io_opt = lcm_not_zero(t->io_opt, b->io_opt); - t->chunk_sectors = lcm_not_zero(t->chunk_sectors, b->chunk_sectors); + + /* Set non-power-of-2 compatible chunk_sectors boundary */ + if (b->chunk_sectors) + t->chunk_sectors = gcd(t->chunk_sectors, b->chunk_sectors);

/* Physical block size a multiple of the logical block size? */ if (t->physical_block_size & (t->logical_block_size - 1)) {