From cbab0e4eec299e9059199ebe6daf48730be46d2b Mon Sep 17 00:00:00 2001 From: Rafael Aquini Date: Wed, 12 Jun 2013 14:04:49 -0700 Subject: [PATCH] swap: avoid read_swap_cache_async() race to deadlock while waiting on discard I/O completion read_swap_cache_async() can race against get_swap_page(), and stumble across a SWAP_HAS_CACHE entry in the swap map whose page wasn't brought into the swapcache yet. This transient swap_map state is expected to be transitory, but the actual placement of discard at scan_swap_map() inserts a wait for I/O completion thus making the thread at read_swap_cache_async() to loop around its -EEXIST case, while the other end at get_swap_page() is scheduled away at scan_swap_map(). This can leave the system deadlocked if the I/O completion happens to be waiting on the CPU waitqueue where read_swap_cache_async() is busy looping and !CONFIG_PREEMPT. This patch introduces a cond_resched() call to make the aforementioned read_swap_cache_async() busy loop condition to bail out when necessary, thus avoiding the subtle race window. Signed-off-by: Rafael Aquini Acked-by: Johannes Weiner Acked-by: KOSAKI Motohiro Acked-by: Hugh Dickins Cc: Shaohua Li Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-format-patch failed