mm: allow drivers to prevent new writable mappings
authorDavid Herrmann <>
Fri, 8 Aug 2014 21:25:25 +0000 (14:25 -0700)
committerGrazvydas Ignotas <>
Sat, 16 Sep 2017 21:29:32 +0000 (00:29 +0300)
This patch (of 6):

The i_mmap_writable field counts existing writable mappings of an
address_space.  To allow drivers to prevent new writable mappings, make
this counter signed and prevent new writable mappings if it is negative.
This is modelled after i_writecount and DENYWRITE.

This will be required by the shmem-sealing infrastructure to prevent any
new writable mappings after the WRITE seal has been set.  In case there
exists a writable mapping, this operation will fail with EBUSY.

Note that we rely on the fact that iff you already own a writable mapping,
you can increase the counter without using the helpers.  This is the same
that we do for i_writecount.

Signed-off-by: David Herrmann <>
Acked-by: Hugh Dickins <>
Cc: Michael Kerrisk <>
Cc: Ryan Lortie <>
Cc: Lennart Poettering <>
Cc: Daniel Mack <>
Cc: Andy Lutomirski <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>

No differences found