process_prepared_discard_passdown_pt1() should cleanup dm_thin_new_mapping in cases of error.
dm_pool_inc_data_range() can fail trying to get a block reference: metadata operation 'dm_pool_inc_data_range' failed: error = -61 When dm_pool_inc_data_range() fails, dm thin aborts current metadata transaction and marks pool as PM_READ_ONLY. Memory for thin mapping is released as well. However, current thin mapping will be queued onto next stage as part of queue_passdown_pt2() or passdown_endio(). This dangling thin mapping memory when processed and accessed in next stage will lead to device mapper crashing. Code flow without fix: -> process_prepared_discard_passdown_pt1(m) -> dm_thin_remove_range() -> discard passdown --> passdown_endio(m) queues m onto next stage -> dm_pool_inc_data_range() fails, frees memory m but does not remove it from next stage queue -> process_prepared_discard_passdown_pt2(m) -> processes freed memory m and crashes One such stack: Call Trace: [<ffffffffa037a46f>] dm_cell_release_no_holder+0x2f/0x70 [dm_bio_prison] [<ffffffffa039b6dc>] cell_defer_no_holder+0x3c/0x80 [dm_thin_pool] [<ffffffffa039b88b>] process_prepared_discard_passdown_pt2+0x4b/0x90 [dm_thin_pool] [<ffffffffa0399611>] process_prepared+0x81/0xa0 [dm_thin_pool] [<ffffffffa039e735>] do_worker+0xc5/0x820 [dm_thin_pool] [<ffffffff8152bf54>] ? __schedule+0x244/0x680 [<ffffffff81087e72>] ? pwq_activate_delayed_work+0x42/0xb0 [<ffffffff81089f53>] process_one_work+0x153/0x3f0 [<ffffffff8108a71b>] worker_thread+0x12b/0x4b0 [<ffffffff8108a5f0>] ? rescuer_thread+0x350/0x350 [<ffffffff8108fd6a>] kthread+0xca/0xe0 [<ffffffff8108fca0>] ? kthread_park+0x60/0x60 [<ffffffff81530b45>] ret_from_fork+0x25/0x30 The fix is to first take the block ref count for discarded block and then do a passdown discard of this block. If block ref count fails, then bail out aborting current metadata transaction, mark pool as PM_READ_ONLY and also free current thin mapping memory (existing error handling code) without queueing this thin mapping onto next stage of processing. If block ref count succeeds, then passdown discard of this block. Discard callback of passdown_endio() will queue this thin mapping onto next stage of processing. Code flow with fix: -> process_prepared_discard_passdown_pt1(m) -> dm_thin_remove_range() -> dm_pool_inc_data_range() --> if fails, free memory m and bail out -> discard passdown --> passdown_endio(m) queues m onto next stage Cc: stable <sta...@vger.kernel.org> # v4.9+ Reviewed-by: Eduardo Valentin <edu...@amazon.com> Reviewed-by: Cristian Gafton <gaf...@amazon.com> Reviewed-by: Anchal Agarwal <ancha...@amazon.com> Signed-off-by: Vallish Vaidyeshwara <vall...@amazon.com> --- drivers/md/dm-thin.c | 26 +++++++++++++------------- 1 file changed, 13 insertions(+), 13 deletions(-) diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c index 17ad50d..28808e5 100644 --- a/drivers/md/dm-thin.c +++ b/drivers/md/dm-thin.c @@ -1094,6 +1094,19 @@ static void process_prepared_discard_passdown_pt1(struct dm_thin_new_mapping *m) return; } + /* + * Increment the unmapped blocks. This prevents a race between the + * passdown io and reallocation of freed blocks. + */ + r = dm_pool_inc_data_range(pool->pmd, m->data_block, data_end); + if (r) { + metadata_operation_failed(pool, "dm_pool_inc_data_range", r); + bio_io_error(m->bio); + cell_defer_no_holder(tc, m->cell); + mempool_free(m, pool->mapping_pool); + return; + } + discard_parent = bio_alloc(GFP_NOIO, 1); if (!discard_parent) { DMWARN("%s: unable to allocate top level discard bio for passdown. Skipping passdown.", @@ -1114,19 +1127,6 @@ static void process_prepared_discard_passdown_pt1(struct dm_thin_new_mapping *m) end_discard(&op, r); } } - - /* - * Increment the unmapped blocks. This prevents a race between the - * passdown io and reallocation of freed blocks. - */ - r = dm_pool_inc_data_range(pool->pmd, m->data_block, data_end); - if (r) { - metadata_operation_failed(pool, "dm_pool_inc_data_range", r); - bio_io_error(m->bio); - cell_defer_no_holder(tc, m->cell); - mempool_free(m, pool->mapping_pool); - return; - } } static void process_prepared_discard_passdown_pt2(struct dm_thin_new_mapping *m) -- 2.7.3.AMZN -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel