On 2020-01-23 11:17:13, Stefan Bader wrote: > When device-mapper adapted for multi-queue functionality, they > also re-organized the way the make-request function was set. > Before, this happened when the device-mapper logical device was > created. Now it is done once the mapping table gets loaded the > first time (this also decides whether the block device is request > or bio based). > > However in generic_make_request(), the request function gets used > without further checks and this happens if one tries to mount such > a partially set up device. > > This can easily be reproduced with the following steps: > - dmsetup create -n test > - mount /dev/dm-<#> /mnt > > This maybe is something which also should be fixed up in device- > mapper. But given there is already a check for an unset queue > pointer and potentially there could be other drivers which do or > might do the same, it sounds like a good move to add another check > to generic_make_request_checks() and to bail out if the request > function has not been set, yet. > > BugLink: https://bugs.launchpad.net/bugs/1860231 > Fixes: ff36ab34583a ("dm: remove request-based logic from make_request_fn wrapper") > Signed-off-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx> I helped debug the crash with Stefan and I think this is the most straightforward fix (and is trivial to backport for stable kernels). I looked at delaying the queue allocation in the dm code until the table load ioctl but I decided that was risky and doesn't help the general case of preventing other subsystems from making this same mistake. Tested-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxx> Reviewed-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxx> Tyler > --- > block/blk-core.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/block/blk-core.c b/block/blk-core.c > index 1075aaff606d..adcd042edd2d 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -884,6 +884,13 @@ generic_make_request_checks(struct bio *bio) > bio_devname(bio, b), (long long)bio->bi_iter.bi_sector); > goto end_io; > } > + if (unlikely(!q->make_request_fn)) { > + printk(KERN_ERR > + "generic_make_request: Trying to access " > + "block-device without request function: %s\n", > + bio_devname(bio, b)); > + goto end_io; > + } > > /* > * Non-mq queues do not honor REQ_NOWAIT, so complete a bio > -- > 2.17.1 >
