prctl_set_mm: downgrade mmap_sem to read lock

The commit a3b609ef9f8b ("proc read mm's {arg,env}_{start,end} with mmap
semaphore taken.") added synchronization of reading argument/environment
boundaries under mmap_sem.  Later commit 88aa7cc688d4 ("mm: introduce
arg_lock to protect arg_start|end and env_start|end in mm_struct") avoided
the coarse use of mmap_sem in similar situations.  But there still
remained two places that (mis)use mmap_sem.

get_cmdline should also use arg_lock instead of mmap_sem when it reads the
boundaries.

The second place that should use arg_lock is in prctl_set_mm.  By
protecting the boundaries fields with the arg_lock, we can downgrade
mmap_sem to reader lock (analogous to what we already do in
prctl_set_mm_map).

[[email protected]: coding style fixes]
Link: http://lkml.kernel.org/r/[email protected]
Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct")
Signed-off-by: Michal Koutný <[email protected]>
Signed-off-by: Laurent Dufour <[email protected]>
Co-developed-by: Laurent Dufour <[email protected]>
Reviewed-by: Cyrill Gorcunov <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Mateusz Guzik <[email protected]>
Cc: Kirill Tkhai <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions