From 9c1cc2e4f25c14dc1a2d98e98808aefef24abaf4 Mon Sep 17 00:00:00 2001 From: Huang Ying Date: Wed, 3 May 2017 14:54:33 -0700 Subject: [PATCH] mm, swap: fix comment in __read_swap_cache_async Commit cbab0e4eec29 ("swap: avoid read_swap_cache_async() race to deadlock while waiting on discard I/O completion") fixed a deadlock in read_swap_cache_async(). Because at that time, in swap allocation path, a swap entry may be set as SWAP_HAS_CACHE, then wait for discarding to complete before the page for the swap entry is added to the swap cache. But in commit 815c2c543d3a ("swap: make swap discard async"), the discarding for swap become asynchronous, waiting for discarding to complete will be done before the swap entry is set as SWAP_HAS_CACHE. So the comments in code is incorrect now. This patch fixes the comments. The cond_resched() added in the commit cbab0e4eec29 is not necessary now too. But if we added some sleep in swap allocation path in the future, there may be some hard to debug/reproduce deadlock bug. So it is kept. Link: http://lkml.kernel.org/r/20170317064635.12792-1-ying.huang@intel.com Signed-off-by: "Huang, Ying" Acked-by: Rafael Aquini Cc: Shaohua Li Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swap_state.c | 12 +----------- 1 file changed, 1 insertion(+), 11 deletions(-) diff --git a/mm/swap_state.c b/mm/swap_state.c index 473b71e052a8..7bfb9bd1ca21 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -360,17 +360,7 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, /* * We might race against get_swap_page() and stumble * across a SWAP_HAS_CACHE swap_map entry whose page - * has not been brought into the swapcache yet, while - * the other end is scheduled away waiting on discard - * I/O completion at scan_swap_map(). - * - * In order to avoid turning this transitory state - * into a permanent loop around this -EEXIST case - * if !CONFIG_PREEMPT and the I/O completion happens - * to be waiting on the CPU waitqueue where we are now - * busy looping, we just conditionally invoke the - * scheduler here, if there are some more important - * tasks to run. + * has not been brought into the swapcache yet. */ cond_resched(); continue; -- 2.20.1