Messages in this thread | | | Date | Tue, 26 Jul 2011 09:15:56 -0700 | Subject | Re: Preempt & smp_processor_id in __make_request | From | "Williams, Dan J" <> |
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On Tue, Jul 26, 2011 at 3:56 AM, Sergey Senozhatsky <sergey.senozhatsky@gmail.com> wrote: > On (07/26/11 10:32), Steven Whitehouse wrote: >> Jul 26 09:54:04 chywoon kernel: BUG: using smp_processor_id() in preemptible [00 >> 000000] code: jbd2/dm-0-8/1546 >> Jul 26 09:54:04 chywoon kernel: caller is __make_request+0x209/0x350 >> Jul 26 09:54:04 chywoon kernel: Pid: 1546, comm: jbd2/dm-0-8 Tainted: G W >> 3.0.0+ #252 >> Jul 26 09:54:04 chywoon kernel: Call Trace: >> Jul 26 09:54:04 chywoon kernel: [<ffffffff813db897>] debug_smp_processor_id+0xe7 >> /0x100 >> Jul 26 09:54:04 chywoon kernel: [<ffffffff813b6f29>] __make_request+0x209/0x350 >> Jul 26 09:54:04 chywoon kernel: [<ffffffff8154635e>] ? dm_request+0x2e/0x280 >> Jul 26 09:54:04 chywoon kernel: [<ffffffff813b3ffb>] generic_make_request+0x27b/ >> 0x550 >> Jul 26 09:54:04 chywoon kernel: [<ffffffff8123ef7e>] ? jbd2_journal_file_buffer+ >> 0x8e/0x130 >> Jul 26 09:54:04 chywoon kernel: [<ffffffff813b432f>] submit_bio+0x5f/0xd0 >> Jul 26 09:54:04 chywoon kernel: [<ffffffff811b14a6>] submit_bh+0xe6/0x120 >> etc. >> >> The (trivial) fix appears to be the following: >> >> diff --git a/block/blk-core.c b/block/blk-core.c >> index f8cb099..f925581 100644 >> --- a/block/blk-core.c >> +++ b/block/blk-core.c >> @@ -1283,7 +1283,7 @@ get_rq: >> >> if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) || >> bio_flagged(bio, BIO_CPU_AFFINE)) >> - req->cpu = smp_processor_id(); >> + req->cpu = raw_smp_processor_id(); >> >> plug = current->plug; >> if (plug) { >> >> However this fixes the symptoms, rather than the cause, so I'm not at >> all sure that this is the correct solution,
I did not realize smp_processor_id() enforced that restriction. It seems like we want raw_smp_processor_id() since it is an affinity hint, and not an affinity guarantee.
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