|author||Huang Ying <firstname.lastname@example.org>||2017-05-03 14:54:33 -0700|
|committer||Linus Torvalds <email@example.com>||2017-05-03 15:52:10 -0700|
|parent||mm: remove SWAP_[SUCCESS|AGAIN|FAIL] (diff)|
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://firstname.lastname@example.org Signed-off-by: "Huang, Ying" <email@example.com> Acked-by: Rafael Aquini <firstname.lastname@example.org> Cc: Shaohua Li <email@example.com> Signed-off-by: Andrew Morton <firstname.lastname@example.org> Signed-off-by: Linus Torvalds <email@example.com>
Diffstat (limited to 'mm/swap_state.c')
1 files changed, 1 insertions, 11 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 473b71e052a8..7bfb9bd1ca21 100644
@@ -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.