[LU-3471] "client_obd_lock_t cl_loi_list_lock" in struct client_obd should not be a spin lock (b1_8)

• Type: Bug
• Resolution: Cannot Reproduce
• Priority: Minor
• Labels: patch
• Severity: 3
• Assignee: Keith Mannthey (Inactive)
• Reporter: Vladimir Saveliev

Description

client_obd_lock_t cl_loi_list_lock of struct client_obd is used to protect async page operations which are not guaranteed to not block even on linux, therefore
spinlock (used for linux implementaion of cl_loi_list_lock) is not appropriate.

For example, in the call chain:
osc_check_rpcs() -> osc_send_oap_rpc() -> ptlrpcd_add_req():

osc_check_rpc() is called with cli->cl_loi_list_lock spinlock held and
ptlrpcd_add_req() may wait with timeout.

In http://jira-nss.xy01.xyratex.com:8080/browse/MRP-1053 there was discovered a hang cause by scheduling from a process holding the cl_loi_list_lock.
Corresponding core dump is removed already, and I do not remember exactly it hung that time.

In new kernels, 3.0.42, the following call chain may block:
osc_check_rpcs() -> osc_send_oap_rpc() -> ll_ap_make_ready() -> clear_page_dirty_for_io() -> page_mkclean() -> page_mkclean_file()

page_mkclean_file() locks mutex:
mutex_lock(&mapping->i_mmap_mutex);

See http://jira-nss.xy01.xyratex.com:8080/browse/LELUS-116 for more details