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There is a problem with the way mirrors have been designed to handle failures that is resulting in stuck LVM processes and hung I/O. When mirrors encounter a write failure, they block I/O and notify userspace to reconfigure the mirror to remove failed devices. This process is open to a couple races: 1) Any LVM process other than the one that is meant to deal with the mirror failure can attempt to read the mirror, fail, and block other LVM commands (including the repair command) from proceeding due to holding a lock on the volume group. 2) If there are multiple mirrors that suffer a failure in the same volume group, a repair can block while attempting to read the LVM label from one mirror while trying to repair the other. Mitigation of these races has been attempted by disallowing label reading of mirrors that are either suspended or are indicated as blocking by the kernel. While this has closed the window of opportunity for hitting the above problems considerably, it hasn't closed it completely. This is because it is still possible to start an LVM command, read the status of the mirror as healthy, and then perform the read for the label at the moment after a the failure is discovered by the kernel. I can see two solutions to this problem: 1) Allow users to configure whether mirrors can be candidates for LVM labels (i.e. whether PVs can be created on mirror LVs). If the user chooses to allow label scanning of mirror LVs, it will be at the expense of a possible hang in I/O or LVM processes. 2) Instrument a way to allow asynchronous label reading - allowing blocked label reads to be ignored while continuing to process the LVM command. This would action would allow LVM commands to continue even though they would have otherwise blocked trying to read a mirror. They can then release their lock and allow a repair command to commence. In the event of #2 above, the repair command already in progress can continue and repair the failed mirror. This patch brings solution #1. If solution #2 is developed later on, the configuration option created in #1 can be negated - allowing mirrors to be scanned for labels by default once again.
87 lines
2.7 KiB
C
87 lines
2.7 KiB
C
/*
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* Copyright (C) 2001-2004 Sistina Software, Inc. All rights reserved.
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* Copyright (C) 2004-2011 Red Hat, Inc. All rights reserved.
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*
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* This file is part of LVM2.
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*
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* This copyrighted material is made available to anyone wishing to use,
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* modify, copy, or redistribute it subject to the terms and conditions
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* of the GNU Lesser General Public License v.2.1.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program; if not, write to the Free Software Foundation,
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* Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#ifndef _LVM_GLOBALS_H
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#define _LVM_GLOBALS_H
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#define VERBOSE_BASE_LEVEL _LOG_WARN
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#define SECURITY_LEVEL 0
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#define PV_MIN_SIZE_KB 512
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void init_verbose(int level);
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void init_silent(int silent);
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void init_test(int level);
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void init_md_filtering(int level);
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void init_pvmove(int level);
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void init_full_scan_done(int level);
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void init_obtain_device_list_from_udev(int device_list_from_udev);
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void init_trust_cache(int trustcache);
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void init_debug(int level);
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void init_debug_classes_logged(int classes);
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void init_cmd_name(int status);
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void init_ignorelockingfailure(int level);
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void init_lockingfailed(int level);
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void init_security_level(int level);
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void init_mirror_in_sync(int in_sync);
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void init_dmeventd_monitor(int reg);
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void init_background_polling(int polling);
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void init_ignore_suspended_devices(int ignore);
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void init_ignore_lvm_mirrors(int scan);
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void init_error_message_produced(int produced);
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void init_is_static(unsigned value);
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void init_udev_checking(int checking);
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void init_dev_disable_after_error_count(int value);
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void init_pv_min_size(uint64_t sectors);
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void init_activation_checks(int checks);
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void init_detect_internal_vg_cache_corruption(int detect);
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void init_retry_deactivation(int retry);
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void set_cmd_name(const char *cmd_name);
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void set_sysfs_dir_path(const char *path);
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int test_mode(void);
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int md_filtering(void);
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int pvmove_mode(void);
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int full_scan_done(void);
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int obtain_device_list_from_udev(void);
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int trust_cache(void);
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int verbose_level(void);
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int silent_mode(void);
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int debug_level(void);
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int debug_class_is_logged(int class);
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int ignorelockingfailure(void);
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int lockingfailed(void);
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int security_level(void);
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int mirror_in_sync(void);
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int background_polling(void);
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int ignore_suspended_devices(void);
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int ignore_lvm_mirrors(void);
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const char *log_command_name(void);
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unsigned is_static(void);
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int udev_checking(void);
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const char *sysfs_dir_path(void);
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uint64_t pv_min_size(void);
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int activation_checks(void);
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int detect_internal_vg_cache_corruption(void);
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int retry_deactivation(void);
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#define DMEVENTD_MONITOR_IGNORE -1
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int dmeventd_monitor_mode(void);
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#define NO_DEV_ERROR_COUNT_LIMIT 0
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int dev_disable_after_error_count(void);
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#endif
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