Re: [PATCH -next 3/6] md/raid1: remove rcu protection to access rdev from conf
From: Song Liu <song@kernel.org>
Date: 2023-10-18 17:57:16
Also in:
lkml
On Sun, Oct 15, 2023 at 6:28 PM Yu Kuai [off-list ref] wrote:
From: Yu Kuai <redacted> It's safe to accees rdev from conf: - If any spinlock is held, because synchronize_rcu() from md_kick_rdev_from_array() will prevent 'rdev' to be freed until spinlock is released; - If 'reconfig_lock' is held, because rdev can't be added or removed from array;
Maybe add lockdep asserts for the above cases? Thanks, Song
quoted hunk ↗ jump to hunk
- If there is normal IO inflight, because mddev_suspend() will prevent rdev to be added or removed from array; - If there is sync IO inflight, because 'MD_RECOVERY_RUNNING' is checked in remove_and_add_spares(). And these will cover all the scenarios in raid1. Signed-off-by: Yu Kuai <redacted> --- drivers/md/raid1.c | 57 +++++++++++++++++----------------------------- 1 file changed, 21 insertions(+), 36 deletions(-)diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c index 4348d670439d..5c647036663d 100644 --- a/drivers/md/raid1.c +++ b/drivers/md/raid1.c@@ -609,7 +609,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect int choose_first; int choose_next_idle; - rcu_read_lock(); /* * Check if we can balance. We can balance on the whole * device if no resync is going on, or below the resync window.@@ -642,7 +641,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect unsigned int pending; bool nonrot; - rdev = rcu_dereference(conf->mirrors[disk].rdev); + rdev = conf->mirrors[disk].rdev; if (r1_bio->bios[disk] == IO_BLOCKED || rdev == NULL || test_bit(Faulty, &rdev->flags))@@ -773,7 +772,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect } if (best_disk >= 0) { - rdev = rcu_dereference(conf->mirrors[best_disk].rdev); + rdev = conf->mirrors[best_disk].rdev; if (!rdev) goto retry; atomic_inc(&rdev->nr_pending);@@ -784,7 +783,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect conf->mirrors[best_disk].next_seq_sect = this_sector + sectors; } - rcu_read_unlock(); *max_sectors = sectors; return best_disk;@@ -1235,14 +1233,12 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio, if (r1bio_existed) { /* Need to get the block device name carefully */ - struct md_rdev *rdev; - rcu_read_lock(); - rdev = rcu_dereference(conf->mirrors[r1_bio->read_disk].rdev); + struct md_rdev *rdev = conf->mirrors[r1_bio->read_disk].rdev; + if (rdev) snprintf(b, sizeof(b), "%pg", rdev->bdev); else strcpy(b, "???"); - rcu_read_unlock(); } /*@@ -1396,10 +1392,9 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio, disks = conf->raid_disks * 2; blocked_rdev = NULL; - rcu_read_lock(); max_sectors = r1_bio->sectors; for (i = 0; i < disks; i++) { - struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev); + struct md_rdev *rdev = conf->mirrors[i].rdev; /* * The write-behind io is only attempted on drives marked as@@ -1465,7 +1460,6 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio, } r1_bio->bios[i] = bio; } - rcu_read_unlock(); if (unlikely(blocked_rdev)) { /* Wait for this device to become unblocked */@@ -1617,15 +1611,16 @@ static void raid1_status(struct seq_file *seq, struct mddev *mddev) struct r1conf *conf = mddev->private; int i; + lockdep_assert_held(&mddev->lock); + seq_printf(seq, " [%d/%d] [", conf->raid_disks, conf->raid_disks - mddev->degraded); - rcu_read_lock(); for (i = 0; i < conf->raid_disks; i++) { - struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev); + struct md_rdev *rdev = READ_ONCE(conf->mirrors[i].rdev); + seq_printf(seq, "%s", rdev && test_bit(In_sync, &rdev->flags) ? "U" : "_"); } - rcu_read_unlock(); seq_printf(seq, "]"); }@@ -1785,7 +1780,7 @@ static int raid1_add_disk(struct mddev *mddev, struct md_rdev *rdev) */ if (rdev->saved_raid_disk < 0) conf->fullsync = 1; - rcu_assign_pointer(p->rdev, rdev); + WRITE_ONCE(p->rdev, rdev); break; } if (test_bit(WantReplacement, &p->rdev->flags) &&@@ -1801,7 +1796,7 @@ static int raid1_add_disk(struct mddev *mddev, struct md_rdev *rdev) rdev->raid_disk = repl_slot; err = 0; conf->fullsync = 1; - rcu_assign_pointer(p[conf->raid_disks].rdev, rdev); + WRITE_ONCE(p[conf->raid_disks].rdev, rdev); } return err;@@ -1835,7 +1830,7 @@ static int raid1_remove_disk(struct mddev *mddev, struct md_rdev *rdev) err = -EBUSY; goto abort; } - p->rdev = NULL; + WRITE_ONCE(p->rdev, NULL); if (conf->mirrors[conf->raid_disks + number].rdev) { /* We just removed a device that is being replaced. * Move down the replacement. We drain all IO before@@ -1856,7 +1851,7 @@ static int raid1_remove_disk(struct mddev *mddev, struct md_rdev *rdev) goto abort; } clear_bit(Replacement, &repl->flags); - p->rdev = repl; + WRITE_ONCE(p->rdev, repl); conf->mirrors[conf->raid_disks + number].rdev = NULL; unfreeze_array(conf); }@@ -2253,8 +2248,7 @@ static void fix_read_error(struct r1conf *conf, int read_disk, sector_t first_bad; int bad_sectors; - rcu_read_lock(); - rdev = rcu_dereference(conf->mirrors[d].rdev); + rdev = conf->mirrors[d].rdev; if (rdev && (test_bit(In_sync, &rdev->flags) || (!test_bit(Faulty, &rdev->flags) &&@@ -2262,15 +2256,14 @@ static void fix_read_error(struct r1conf *conf, int read_disk, is_badblock(rdev, sect, s, &first_bad, &bad_sectors) == 0) { atomic_inc(&rdev->nr_pending); - rcu_read_unlock(); if (sync_page_io(rdev, sect, s<<9, conf->tmppage, REQ_OP_READ, false)) success = 1; rdev_dec_pending(rdev, mddev); if (success) break; - } else - rcu_read_unlock(); + } + d++; if (d == conf->raid_disks * 2) d = 0;@@ -2289,29 +2282,24 @@ static void fix_read_error(struct r1conf *conf, int read_disk, if (d==0) d = conf->raid_disks * 2; d--; - rcu_read_lock(); - rdev = rcu_dereference(conf->mirrors[d].rdev); + rdev = conf->mirrors[d].rdev; if (rdev && !test_bit(Faulty, &rdev->flags)) { atomic_inc(&rdev->nr_pending); - rcu_read_unlock(); r1_sync_page_io(rdev, sect, s, conf->tmppage, WRITE); rdev_dec_pending(rdev, mddev); - } else - rcu_read_unlock(); + } } d = start; while (d != read_disk) { if (d==0) d = conf->raid_disks * 2; d--; - rcu_read_lock(); - rdev = rcu_dereference(conf->mirrors[d].rdev); + rdev = conf->mirrors[d].rdev; if (rdev && !test_bit(Faulty, &rdev->flags)) { atomic_inc(&rdev->nr_pending); - rcu_read_unlock(); if (r1_sync_page_io(rdev, sect, s, conf->tmppage, READ)) { atomic_add(s, &rdev->corrected_errors);@@ -2322,8 +2310,7 @@ static void fix_read_error(struct r1conf *conf, int read_disk, rdev->bdev); } rdev_dec_pending(rdev, mddev); - } else - rcu_read_unlock(); + } } sectors -= s; sect += s;@@ -2704,7 +2691,6 @@ static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr, r1_bio = raid1_alloc_init_r1buf(conf); - rcu_read_lock(); /* * If we get a correctably read error during resync or recovery, * we might want to read from a different device. So we@@ -2725,7 +2711,7 @@ static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr, struct md_rdev *rdev; bio = r1_bio->bios[i]; - rdev = rcu_dereference(conf->mirrors[i].rdev); + rdev = conf->mirrors[i].rdev; if (rdev == NULL || test_bit(Faulty, &rdev->flags)) { if (i < conf->raid_disks)@@ -2783,7 +2769,6 @@ static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr, bio->bi_opf |= MD_FAILFAST; } } - rcu_read_unlock(); if (disk < 0) disk = wonly; r1_bio->read_disk = disk; --2.39.2