On Thu, Sep 28, 2017 at 08:39:31AM -0400, Mimi Zohar wrote:

Writing extended attributes requires exclusively taking the i_rwsem
lock.  To synchronize the file hash calculation and writing the file
hash as security.ima xattr, IMA-appraisal takes the i_rwsem lock
exclusively before calculating the file hash.  (Once the file hash
is calculated, the result is cached.  Taking the lock exclusively
prevents calculating the file hash multiple times.)

Some filesystems have recently replaced their filesystem dependent
lock with the global i_rwsem to read a file.  As a result, when IMA
attempts to calculate the file hash, reading the file attempts to
take the i_rwsem again.

To resolve this problem, this patch defines a new read_iter flag
named "rwf" to indicate that the i_rwsem has already been taken
exclusively.  Subsequent patches will set or test the "rwf" flag.

I don't like adding a bool parameter everywhere.  Why not add a flag
to the kiocb ki_flags?

#define IOCB_RWSEM_HELD		(1 << 8)