scsi: target: core: Fix race during ACL removal
Under huge load there is a possibility of race condition in updating
se_dev_entry object in ACL removal procedure:
NIP [
c0080000154093d0] transport_lookup_cmd_lun+0x1f8/0x3d0 [target_core_mod]
LR [
c00800001542ab34] target_submit_cmd_map_sgls+0x11c/0x300 [target_core_mod]
Call Trace:
target_submit_cmd_map_sgls+0x11c/0x300 [target_core_mod]
target_submit_cmd+0x44/0x60 [target_core_mod]
tcm_qla2xxx_handle_cmd+0x88/0xe0 [tcm_qla2xxx]
qlt_do_work+0x2e4/0x3d0 [qla2xxx]
process_one_work+0x298/0x5c
Despite usage of RCU primitives with deve->se_lun pointer, it has not
become dereference-safe because deve->se_lun is updated and not
synchronized with a reader. That change might be in a release function
called by synchronize_rcu(). But, in fact, there is no point in setting
that pointer to NULL for deleting deve. All access to deve->se_lun is
already under rcu_read_lock. And either deve->se_lun is always valid or
deve is not valid itself and will not be found in the list_for_*. The same
applicable for deve->se_lun_acl too. So a better solution is to remove
that NULLing.
Link: https://lore.kernel.org/r/20220727214125.19647-2-d.bogdanov@yadro.com
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>