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authorNeilBrown <neilb@suse.de>2015-02-13 15:49:17 +1100
committerIngo Molnar <mingo@kernel.org>2015-02-18 14:27:44 +0100
commit9cff8adeaa34b5d2802f03f89803da57856b3b72 (patch)
treeb23f52785c2f1fef1577a4cdf238389bec7e63c1 /include/linux/sched.h
parentbc9560155f4063bbc9be71bd69d6726d41b47653 (diff)
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 <neilb@suse.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> [ Moved the now rudimentary io_schedule() into sched.h. ] Cc: Jens Axboe <axboe@kernel.dk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Tony Battersby <tonyb@cybernetics.com> Link: http://lkml.kernel.org/r/20150213162600.059fffb2@notabene.brown Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/sched.h')
-rw-r--r--include/linux/sched.h10
1 files changed, 7 insertions, 3 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8db31ef98d2f..cb5cdc777c8a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -363,9 +363,6 @@ extern void show_regs(struct pt_regs *);
*/
extern void show_stack(struct task_struct *task, unsigned long *sp);
-void io_schedule(void);
-long io_schedule_timeout(long timeout);
-
extern void cpu_init (void);
extern void trap_init(void);
extern void update_process_times(int user);
@@ -422,6 +419,13 @@ extern signed long schedule_timeout_uninterruptible(signed long timeout);
asmlinkage void schedule(void);
extern void schedule_preempt_disabled(void);
+extern long io_schedule_timeout(long timeout);
+
+static inline void io_schedule(void)
+{
+ io_schedule_timeout(MAX_SCHEDULE_TIMEOUT);
+}
+
struct nsproxy;
struct user_namespace;