From: NeilBrown Date: Fri, 13 Feb 2015 04:49:17 +0000 (+1100) Subject: sched: Prevent recursion in io_schedule() X-Git-Tag: fixes-v4.0-rc1~42^2~3 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9cff8adeaa34b5d2802f03f89803da57856b3b72;p=pandora-kernel.git sched: Prevent recursion in io_schedule() io_schedule() calls blk_flush_plug() which, depending on the contents of current->plug, can initiate arbitrary blk-io requests. Note that this contrasts with blk_schedule_flush_plug() which requires all non-trivial work to be handed off to a separate thread. This makes it possible for io_schedule() to recurse, and initiating block requests could possibly call mempool_alloc() which, in times of memory pressure, uses io_schedule(). Apart from any stack usage issues, io_schedule() will not behave correctly when called recursively as delayacct_blkio_start() does not allow for repeated calls. So: - use ->in_iowait to detect recursion. Set it earlier, and restore it to the old value. - move the call to "raw_rq" after the call to blk_flush_plug(). As this is some sort of per-cpu thing, we want some chance that we are on the right CPU - When io_schedule() is called recurively, use blk_schedule_flush_plug() which cannot further recurse. - as this makes io_schedule() a lot more complex and as io_schedule() must match io_schedule_timeout(), but all the changes in io_schedule_timeout() and make io_schedule a simple wrapper for that. Signed-off-by: NeilBrown Signed-off-by: Peter Zijlstra (Intel) [ Moved the now rudimentary io_schedule() into sched.h. ] Cc: Jens Axboe Cc: Linus Torvalds Cc: Tony Battersby Link: http://lkml.kernel.org/r/20150213162600.059fffb2@notabene.brown Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed