(cc dm-devel) On Wed, 11 Feb 2009 17:27:42 +0100 Valentin QUEQUET <v.quequet-techniques@xxxxxxxxx> wrote: > > I've finally found why my computer seems to hang (pause) quite lengthy > when I boot Pristine Linux 2.6.29-rcX... instead of Pristine Linux > 2.6.28.4 (for example). > > The reason is that the cryptographic keys generation for the Device > Mapper takes longer with 2.6.29 than with 2.6.28 under certain > circumstances. So it's device-mapper userspace? Is this new behaviour in recent kernel versions? Some kernel change caused /dev/random accesses to wait for longer before sufficient entropy has been gathered? > To notice a non-negligible delay in the key generation phase, the system > must fit the following both 2 conditions: > > 1) The system PRNG entropy pool must lack of entropy normally brought > in the form of environmental noise. > > 2) The system must initiate its Device-Mapper-Encrypted (dm-crypt) > partitions with boot-time dynamically generated > cryptographic keys using "/dev/random" as key file. (the 3rd > field of "/etc/crypttab" ; see "man crypttab") > > > Such a long delay in the key generation phase can be avoided if the > system fits either of the following 2 conditions: > > 1) The excitated user stresses its keyboard and mouse (generates much > environmental noise) to provide the PRNG entropy pool with much entropy. > (Or some other peripheral generates noise : network interface, ...) > > 2) The system initiates dm-crypt partitions using "/dev/urandom" as > key file. > > > But in the scenario where both > 1) environmental noise is reduced to the minimum (no user > 'excitation' and mouse and NIC unplugged) > and > 2) where dm-crypt partitions are initialized with "/dev/random" as > key file, > there is a huge difference whether I boot Linux 2.6.28.y or Linux > 2.6.29-rcX... . > > > In order to provide you with meaningful information but not too much, I > join a few "bootchart"-generated logs (bootchart*.tgz) plus their > ".svgz" corresponding diagrams (Pruned and Not-Pruned) for the following > test cases: > > Having always environmental noise reduced at its minimum possible level. > Using alternately 2.6.28 and 2.6.29 Linux versions. > Using alternately "/dev/random" and "/dev/urandom" as dm-crypt key file. > > There are then 4 test cases for which I join files, and for each test > case, I provide: > - The "bootchart*.tgz" bootchart report. > - The Not-Pruned ".svgz" corresponding SVG diagram. > - The Pruned ".svgz" corresponding SVG diagram. > > Thus leading to the following 12 files: > > -r--r--r-- 1 testr testr 174682 Feb 11 17:10 > DevRandom_bootchart-2.6.28.4.BootChart_Report.tgz > -r--r--r-- 1 testr testr 102648 Feb 11 17:10 > DevRandom_bootchart-2.6.28.4.Not-Pruned_SVG_Diagram.svgz > -r--r--r-- 1 testr testr 26010 Feb 11 17:10 > DevRandom_bootchart-2.6.28.4.Pruned_SVG_Diagram.svgz > -r--r--r-- 1 testr testr 327701 Feb 11 17:10 > DevRandom_bootchart-2.6.29-rc4-git1.BootChart_Report.tgz > -r--r--r-- 1 testr testr 175522 Feb 11 17:10 > DevRandom_bootchart-2.6.29-rc4-git1.Not-Pruned_SVG_Diagram.svgz > -r--r--r-- 1 testr testr 39844 Feb 11 17:10 > DevRandom_bootchart-2.6.29-rc4-git1.Pruned_SVG_Diagram.svgz > -r--r--r-- 1 testr testr 138401 Feb 11 17:10 > DevUrandom_bootchart-2.6.28.4.BootChart_Report.tgz > -r--r--r-- 1 testr testr 80691 Feb 11 17:10 > DevUrandom_bootchart-2.6.28.4.Not-Pruned_SVG_Diagram.svgz > -r--r--r-- 1 testr testr 21136 Feb 11 17:10 > DevUrandom_bootchart-2.6.28.4.Pruned_SVG_Diagram.svgz > -r--r--r-- 1 testr testr 152979 Feb 11 17:10 > DevUrandom_bootchart-2.6.29-rc4-git1.BootChart_Report.tgz > -r--r--r-- 1 testr testr 78323 Feb 11 17:10 > DevUrandom_bootchart-2.6.29-rc4-git1.Not-Pruned_SVG_Diagram.svgz > -r--r--r-- 1 testr testr 20745 Feb 11 17:10 > DevUrandom_bootchart-2.6.29-rc4-git1.Pruned_SVG_Diagram.svgz > > But for the sake of convenience, I tar them all as > "Dev-Random_regression_on_post-2.6.28_kernels.tar" > > In hope my report will prove useful. > > Sincerely, > Valentin QUEQUET > > n.b. : Don't hesitate to ask me for more files or explanations. > -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
