mmap locked doesn't return

mmap locked doesn't return

[Sagar Borikar]

Hi,


We are observing that mmap when called with MAP_SHARED and MAP_LOCKED
flags on the disk which has the bad sectors, doesn't return either
success or failure and gets stuck somewhere in mmap routine. Disk
replacement is the obvious solution but the question is what makes
mmap not to return failure?
Individual mapping works fine i.e. on the same disk at same offset
when mmap is invoked with MAP_SHARED or MAP_LOCKED the call succeeds
but when they both are clubbed together, it doesn't return anything.

strace output snippet

open("/dev/dm-4p2", O_RDWR)             = 3
mmap(NULL, 10485760, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_LOCKED, 3, 0x4000000


setup:

2.6.23 LST kernel
Westmere platform - 4 socket cpu
RAM -192GB


Thanks
Sagar

Re: mmap locked doesn't return

[Hugh Dickins]

On Mon, 23 Jan 2012, Sagar Borikar wrote:
> 
> We are observing that mmap when called with MAP_SHARED and MAP_LOCKED
> flags on the disk which has the bad sectors, doesn't return either
> success or failure and gets stuck somewhere in mmap routine. Disk
> replacement is the obvious solution but the question is what makes
> mmap not to return failure?
> Individual mapping works fine i.e. on the same disk at same offset
> when mmap is invoked with MAP_SHARED or MAP_LOCKED the call succeeds
> but when they both are clubbed together, it doesn't return anything.
> 
> strace output snippet
> 
> open("/dev/dm-4p2", O_RDWR)             = 3
> mmap(NULL, 10485760, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_LOCKED, 3, 0x4000000
> 
> 
> setup:
> 
> 2.6.23 LST kernel
> Westmere platform - 4 socket cpu
> RAM -192GB

2.6.23 is a four-year-old kernel.  There have been a lot of changes
since then, in mlocking and all over.  Here I suspect a change
in filemap_fault() may be relevant.  At the time of 2.6.23, its
page_not_uptodate IO error handling expected an IO error to be
reported by readpage() (which only initiates the read), and looks
in danger of retrying indefinitely.   Whereas in the current tree
I see a wait_on_page_locked() followed by EIO if !PageUptodate there.
My guess is a move to a more recent kernel would solve your problem.

Hugh