On Thu, May 30, 2013 at 2:05 PM, Rafael Aquini <aquini@xxxxxxxxxx> wrote: > 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 workqueue 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 <aquini@xxxxxxxxxx> Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>