From: Huang Ying <ying.huang@xxxxxxxxx>
The 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 the 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.
Cc: Shaohua Li <shli@xxxxxxxxxx>
Cc: Rafael Aquini <aquini@xxxxxxxxxx>
Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
---
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;
--
2.11.0
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