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    SubjectRe: [PATCH resubmit] do_mount: reduce stack consumption
    Adrian Bunk <bunk@stusta.de> wrote:
    >
    > On Fri, Nov 04, 2005 at 10:27:42PM +0100, Heiko Carstens wrote:
    > > > > See original stack back trace below and Andreas' patch and analysis
    > > > > here:
    > > > > http://www.ussg.iu.edu/hypermail/linux/kernel/0410.3/1844.html
    > >
    > > I probably should add that with "original" stack back trace a trace of
    > > a 2.6.10 kernel was meant, if that wasn't clear, but the DM code is
    > > still the same in 2.6.14.
    > >
    > > > > <4>Call Trace:
    > > ...
    > > > > <4> [<0000000010831380>] __map_bio+0x70/0x160 [dm_mod]
    > > > > <4> [<000000001083173e>] __split_bio+0x1e6/0x538 [dm_mod]
    > > > > <4> [<0000000010831ba8>] dm_request+0x118/0x25c [dm_mod]
    > > > > <4> [<0000000000241074>] generic_make_request+0xf0/0x21c
    > > > > <4> [<0000000010831380>] __map_bio+0x70/0x160 [dm_mod]
    > > > > <4> [<000000001083173e>] __split_bio+0x1e6/0x538 [dm_mod]
    > > > > <4> [<0000000010831ba8>] dm_request+0x118/0x25c [dm_mod]
    > > > > <4> [<0000000000241074>] generic_make_request+0xf0/0x21c
    > > > > <4> [<0000000010831380>] __map_bio+0x70/0x160 [dm_mod]
    > > > > <4> [<000000001083173e>] __split_bio+0x1e6/0x538 [dm_mod]
    > > > > <4> [<0000000010831ba8>] dm_request+0x118/0x25c [dm_mod]
    > > > > <4> [<0000000000241074>] generic_make_request+0xf0/0x21c
    > > ...
    > >
    > > This part of the call trace is actually good for >1500 bytes of stack
    > > usage and is what kills us and should be fixed.
    > > I'm surprised that there are no other bug reports regarding DM and
    > > stack overflow with 4k stacks.
    > >...
    >
    > There were some reports of dm+xfs overflows with 4k stacks on i386.
    >
    > The xfs side was sorted out, but I son't know the state of the dm part.
    >

    The state is Very Bad, IMO. At the very least, DM should struggle to the
    utmost to reduce the stack utilisation around that recursion point.
    -
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