From bf15bb38ec7f4ff522da5c20e1673dbda7159938 Mon Sep 17 00:00:00 2001 From: Michal Schmidt Date: Tue, 6 Jun 2023 10:12:53 -0700 Subject: ice: make writes to /dev/gnssX synchronous The current ice driver's GNSS write implementation buffers writes and works through them asynchronously in a kthread. That's bad because: - The GNSS write_raw operation is supposed to be synchronous[1][2]. - There is no upper bound on the number of pending writes. Userspace can submit writes much faster than the driver can process, consuming unlimited amounts of kernel memory. A patch that's currently on review[3] ("[v3,net] ice: Write all GNSS buffers instead of first one") would add one more problem: - The possibility of waiting for a very long time to flush the write work when doing rmmod, softlockups. To fix these issues, simplify the implementation: Drop the buffering, the write_work, and make the writes synchronous. I tested this with gpsd and ubxtool. [1] https://events19.linuxfoundation.org/wp-content/uploads/2017/12/The-GNSS-Subsystem-Johan-Hovold-Hovold-Consulting-AB.pdf "User interface" slide. [2] A comment in drivers/gnss/core.c:gnss_write(): /* Ignoring O_NONBLOCK, write_raw() is synchronous. */ [3] https://patchwork.ozlabs.org/project/intel-wired-lan/patch/20230217120541.16745-1-karol.kolacinski@intel.com/ Fixes: d6b98c8d242a ("ice: add write functionality for GNSS TTY") Signed-off-by: Michal Schmidt Reviewed-by: Simon Horman Tested-by: Sunitha Mekala (A Contingent worker at Intel) Signed-off-by: Tony Nguyen Signed-off-by: David S. Miller --- drivers/net/ethernet/intel/ice/ice_gnss.h | 10 ---------- 1 file changed, 10 deletions(-) (limited to 'drivers/net/ethernet/intel/ice/ice_gnss.h') diff --git a/drivers/net/ethernet/intel/ice/ice_gnss.h b/drivers/net/ethernet/intel/ice/ice_gnss.h index b8bb8b63d081..75e567ad7059 100644 --- a/drivers/net/ethernet/intel/ice/ice_gnss.h +++ b/drivers/net/ethernet/intel/ice/ice_gnss.h @@ -22,26 +22,16 @@ */ #define ICE_GNSS_UBX_WRITE_BYTES (ICE_MAX_I2C_WRITE_BYTES + 1) -struct gnss_write_buf { - struct list_head queue; - unsigned int size; - unsigned char *buf; -}; - /** * struct gnss_serial - data used to initialize GNSS TTY port * @back: back pointer to PF * @kworker: kwork thread for handling periodic work * @read_work: read_work function for handling GNSS reads - * @write_work: write_work function for handling GNSS writes - * @queue: write buffers queue */ struct gnss_serial { struct ice_pf *back; struct kthread_worker *kworker; struct kthread_delayed_work read_work; - struct kthread_work write_work; - struct list_head queue; }; #if IS_ENABLED(CONFIG_GNSS) -- cgit v1.2.3