On Tue, Jul 30, 2024 at 08:31:04AM +0200, Herve Codina wrote:

The carrier_lock spinlock protects the carrier detection. While it is
hold, framer_get_status() is called witch in turn takes a mutex.
This is not correct and can lead to a deadlock.

A run with PROVE_LOCKING enabled detected the issue:
  [ BUG: Invalid wait context ]
  ...
  c204ddbc (&framer->mutex){+.+.}-{3:3}, at: framer_get_status+0x40/0x78
  other info that might help us debug this:
  context-{4:4}
  2 locks held by ifconfig/146:
  #0: c0926a38 (rtnl_mutex){+.+.}-{3:3}, at: devinet_ioctl+0x12c/0x664
  #1: c2006a40 (&qmc_hdlc->carrier_lock){....}-{2:2}, at: qmc_hdlc_framer_set_carrier+0x30/0x98

Avoid the spinlock usage and convert carrier_lock to a mutex.

Fixes: 54762918ca85 ("net: wan: fsl_qmc_hdlc: Add framer support")
Cc: stable@vger.kernel.org
Signed-off-by: Herve Codina <herve.codina@bootlin.com>

Reviewed-by: Simon Horman <horms@kernel.org>