On Thu, 2017-09-28 at 16:39 -0700, Linus Torvalds wrote:
On Thu, Sep 28, 2017 at 3:02 PM, Dave Chinner [off-list ref] wrote:
quoted
On Thu, Sep 28, 2017 at 08:39:33AM -0400, Mimi Zohar wrote:
quoted
Don't attempt to take the i_rwsem, if it has already been taken
exclusively.
Signed-off-by: Mimi Zohar <redacted>
That's bloody awful.
The locking in filesystem IO paths is already complex enough without
adding a new IO path semantic that says "caller has already locked
the i_rwsem in some order and some dependencies that we have no idea
about".
I do have to admit that I never got a satisfactory answer on why IMA
doesn't just use its own private per-inode lock for this all.
It isn't using the i_rwsem for file consistency reasons anyway, so it
seems to be purely about serializing the actual signature generation
with the xattr writing, but since IMA does those both, why isn't IMA
just using its own lock (not the filesystem lock) to do that?
Originally IMA did define it's own lock, prior to IMA-appraisal. ?IMA-
appraisal introduced writing the file hash as an xattr, which required
taking the i_mutex. ?process_measurement() and ima_file_free() took
the iint->mutex first and then the i_mutex, while setxattr, chmod and
chown took the locks in reverse order. ?To resolve the potential
deadlock, the iint->mutex was eliminated.
Mimi
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