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Date: Mon, 13 Feb 2017 15:28:01 -0700 From: Jens Axboe <axboe@...nel.dk> To: Omar Sandoval <osandov@...ndov.com>, Paolo Valente <paolo.valente@...aro.org> Cc: Tejun Heo <tj@...nel.org>, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, ulf.hansson@...aro.org, linus.walleij@...aro.org, broonie@...nel.org Subject: Re: [PATCH BUGFIX] block: make elevator_get robust against cross blk/blk-mq choice On 02/13/2017 03:09 PM, Omar Sandoval wrote: > On Mon, Feb 13, 2017 at 10:01:07PM +0100, Paolo Valente wrote: >> If, at boot, a legacy I/O scheduler is chosen for a device using blk-mq, >> or, viceversa, a blk-mq scheduler is chosen for a device using blk, then >> that scheduler is set and initialized without any check, driving the >> system into an inconsistent state. This commit addresses this issue by >> letting elevator_get fail for these wrong cross choices. >> >> Signed-off-by: Paolo Valente <paolo.valente@...aro.org> >> --- >> block/elevator.c | 26 ++++++++++++++++++-------- >> 1 file changed, 18 insertions(+), 8 deletions(-) > > Hey, Paolo, > > How exactly are you triggering this? In __elevator_change(), we do check > for mq or not mq: > > if (!e->uses_mq && q->mq_ops) { > elevator_put(e); > return -EINVAL; > } > if (e->uses_mq && !q->mq_ops) { > elevator_put(e); > return -EINVAL; > } > > We don't ever appear to call elevator_init() with a specific scheduler > name, and for the default we switch off of q->mq_ops and use the > defaults from Kconfig: > > if (q->mq_ops && q->nr_hw_queues == 1) > e = elevator_get(CONFIG_DEFAULT_SQ_IOSCHED, false); > else if (q->mq_ops) > e = elevator_get(CONFIG_DEFAULT_MQ_IOSCHED, false); > else > e = elevator_get(CONFIG_DEFAULT_IOSCHED, false); > > if (!e) { > printk(KERN_ERR > "Default I/O scheduler not found. " \ > "Using noop/none.\n"); > e = elevator_get("noop", false); > } > > So I guess this could happen if someone manually changed those Kconfig > options, but I don't see what other case would make this happen, could > you please explain? Was wondering the same - is it using the 'elevator=' boot parameter? Didn't look at that path just now, but that's the only one I could think of. If it is, I'd much prefer only using 'chosen_elevator' for the non-mq stuff, and the fix should be just that instead. So instead of: if (!e && *chosen_elevator) { do if (!e && !q->mq_ops && && *chosen_elevator) { -- Jens Axboe
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