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md/r5cache: disable write back for degraded array

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write-back cache in degraded mode introduces corner cases to the array.
Although we try to cover all these corner cases, it is safer to just
disable write-back cache when the array is in degraded mode.

In this patch, we disable writeback cache for degraded mode:
1. On device failure, if the array enters degraded mode, raid5_error()
   will submit async job r5c_disable_writeback_async to disable
   writeback;
2. In r5c_journal_mode_store(), it is invalid to enable writeback in
   degraded mode;
3. In r5c_try_caching_write(), stripes with s->failed>0 will be handled
   in write-through mode.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Shaohua Li <shli@fb.com>
This commit is contained in:
Song Liu 2017-01-24 10:45:30 -08:00 • committed by Shaohua Li
parent 07e8336484
commit 2e38a37f23
3 changed files with 56 additions and 7 deletions
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2
drivers/md/raid5.h
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@ -758,6 +758,7 @@ extern sector_t raid5_compute_sector(struct r5conf *conf, sector_t r_sector,
extern struct stripe_head *
raid5_get_active_stripe(struct r5conf *conf, sector_t sector,
int previous, int noblock, int noquiesce);
extern int raid5_calc_degraded(struct r5conf *conf);
extern int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev);
extern void r5l_exit_log(struct r5l_log *log);
extern int r5l_write_stripe(struct r5l_log *log, struct stripe_head *head_sh);
@ -786,4 +787,5 @@ extern void r5c_flush_cache(struct r5conf *conf, int num);
extern void r5c_check_stripe_cache_usage(struct r5conf *conf);
extern void r5c_check_cached_full_stripe(struct r5conf *conf);
extern struct md_sysfs_entry r5c_journal_mode;
extern void r5c_update_on_rdev_error(struct mddev *mddev);
#endif