Messages in this thread |  | | | Date | Fri, 18 Feb 2005 07:54:14 -0500 | | From | Philip R Auld <> | | Subject | bio refcount problem |
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Hi, I think there are some potential issues with the reference counting of bios as used in 2.6.10. The __make_request function which is the default block device routine accesses the bio structure after issuing the call to add_request. This means that the bio could have completed before __make_request uses it.
The submit_bh path takes an extra reference with an explicit bio_get/put pair around the submit_bio, but many other users of submit_bio do not. Given that most of the end_io routines remove a reference and hence could free the bio this can lead at the least to __make_request mis-reading the sync flag. In more extreme cases it can cause an oops when run with CONFIG_DEBUG_PAGEALLOC.
The question is what is the preferred fix? I think it may be to simply have submit_bio take its own reference (and remove the extra one from submit_bh).
Alternatively __make_request could be adjusted so that it does not access the bio after calling add_request. All it is doing is checking the bi_rw field for the sync bit.
Or make all users of submit_bio take and release and extra reference like submit_bh.
Thoughts?
Cheers,
Phil
-- Philip R. Auld, Ph.D. Egenera, Inc. Software Architect 165 Forest St. (508) 858-2628 Marlboro, MA 01752 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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