[question] why does grok_partitions clear blk_size[major]?

[COTTE@de.ibm.com]

Hi kernel-list-readers!

We just had a problem when running some formatting-utils on
a large amount of disks synchronously: We got a NULL-pointer
violation when accessig blk_size[major] for our major number.
Further research showed, that grok_partitions was running at
that time, which has been called by register_disk, which our
device driver issues after a disk has been formatted.
Grok_partitions first initializes blk_size[major] with a NULL
pointer, detects the partitions and then assigns the original
value to blk_size[major] again.
Can anyone explain to me, why grok_partitions has to clear
this pointer? Why is this all done without any lock which causes
race conditions all over the block-device layer (for example
generic_make_request() in ll_rw_blk.c first checks if the pointer
is set and afterwards accesses the array behind the pointer)?

mit freundlichem Gruß / with kind regards
Carsten Otte

IBM Deutschland Entwicklung GmbH
Linux for 390/zSeries Development - Device Driver Team
Phone: +49/07031/16-4076
IBM internal phone: *120-4076
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