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OpenZFS 8378 - crash due to bp in-memory modification of nopwrite block

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Authored by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: Giuseppe Di Natale <dinatale2@llnl.gov>

The problem is that zfs_get_data() supplies a stale zgd_bp to
dmu_sync(), which we then nopwrite against.
zfs_get_data() doesn't hold any DMU-related locks, so after it
copies db_blkptr to zgd_bp, dbuf_write_ready() could change
db_blkptr, and dbuf_write_done() could remove the dirty record.
dmu_sync() then sees the stale BP and that the dbuf it not dirty,
so it is eligible for nop-writing.
The fix is for dmu_sync() to copy db_blkptr to zgd_bp after
acquiring the db_mtx. We could still see a stale db_blkptr,
but if it is stale then the dirty record will still exist and
thus we won't attempt to nopwrite.

OpenZFS-issue: https://www.illumos.org/issues/8378
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/3127742
Closes #6293
This commit is contained in:
Matthew Ahrens 2017-04-14 12:59:18 -07:00 committed by Brian Behlendorf
parent 8ca78ab002
commit 02dc43bc46
4 changed files with 54 additions and 38 deletions
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7
cmd/ztest/ztest.c
View File

@ -2099,7 +2099,6 @@ ztest_get_data(void *arg, lr_write_t *lr, char *buf, zio_t *zio)
uint64_t object = lr->lr_foid;
uint64_t offset = lr->lr_offset;
uint64_t size = lr->lr_length;
blkptr_t *bp = &lr->lr_blkptr;
uint64_t txg = lr->lr_common.lrc_txg;
uint64_t crtxg;
dmu_object_info_t doi;
@ -2157,11 +2156,7 @@ ztest_get_data(void *arg, lr_write_t *lr, char *buf, zio_t *zio)
DMU_READ_NO_PREFETCH);
if (error == 0) {
blkptr_t *obp = dmu_buf_get_blkptr(db);
if (obp) {
ASSERT(BP_IS_HOLE(bp));
*bp = *obp;
}
blkptr_t *bp = &lr->lr_blkptr;
zgd->zgd_db = db;
zgd->zgd_bp = bp;

60
module/zfs/dmu.c
View File

@ -1561,13 +1561,14 @@ dmu_sync_done(zio_t *zio, arc_buf_t *buf, void *varg)
if (zio->io_error == 0) {
dr->dt.dl.dr_nopwrite = !!(zio->io_flags & ZIO_FLAG_NOPWRITE);
if (dr->dt.dl.dr_nopwrite) {
ASSERTV(blkptr_t *bp = zio->io_bp);
ASSERTV(blkptr_t *bp_orig = &zio->io_bp_orig);
ASSERTV(uint8_t chksum = BP_GET_CHECKSUM(bp_orig));
blkptr_t *bp = zio->io_bp;
blkptr_t *bp_orig = &zio->io_bp_orig;
uint8_t chksum = BP_GET_CHECKSUM(bp_orig);
ASSERT(BP_EQUAL(bp, bp_orig));
VERIFY(BP_EQUAL(bp, db->db_blkptr));
ASSERT(zio->io_prop.zp_compress != ZIO_COMPRESS_OFF);
ASSERT(zio_checksum_table[chksum].ci_flags &
VERIFY(zio_checksum_table[chksum].ci_flags &
ZCHECKSUM_FLAG_NOPWRITE);
}
dr->dt.dl.dr_overridden_by = *zio->io_bp;
@ -1606,20 +1607,12 @@ dmu_sync_late_arrival_done(zio_t *zio)
ASSERTV(blkptr_t *bp_orig = &zio->io_bp_orig);
if (zio->io_error == 0 && !BP_IS_HOLE(bp)) {
/*
* If we didn't allocate a new block (i.e. ZIO_FLAG_NOPWRITE)
* then there is nothing to do here. Otherwise, free the
* newly allocated block in this txg.
*/
if (zio->io_flags & ZIO_FLAG_NOPWRITE) {
ASSERT(BP_EQUAL(bp, bp_orig));
} else {
ASSERT(!(zio->io_flags & ZIO_FLAG_NOPWRITE));
ASSERT(BP_IS_HOLE(bp_orig) || !BP_EQUAL(bp, bp_orig));
ASSERT(zio->io_bp->blk_birth == zio->io_txg);
ASSERT(zio->io_txg > spa_syncing_txg(zio->io_spa));
zio_free(zio->io_spa, zio->io_txg, zio->io_bp);
}
}
dmu_tx_commit(dsa->dsa_tx);
@ -1650,6 +1643,29 @@ dmu_sync_late_arrival(zio_t *pio, objset_t *os, dmu_sync_cb_t *done, zgd_t *zgd,
dsa->dsa_zgd = zgd;
dsa->dsa_tx = tx;
/*
* Since we are currently syncing this txg, it's nontrivial to
* determine what BP to nopwrite against, so we disable nopwrite.
*
* When syncing, the db_blkptr is initially the BP of the previous
* txg. We can not nopwrite against it because it will be changed
* (this is similar to the non-late-arrival case where the dbuf is
* dirty in a future txg).
*
* Then dbuf_write_ready() sets bp_blkptr to the location we will write.
* We can not nopwrite against it because although the BP will not
* (typically) be changed, the data has not yet been persisted to this
* location.
*
* Finally, when dbuf_write_done() is called, it is theoretically
* possible to always nopwrite, because the data that was written in
* this txg is the same data that we are trying to write. However we
* would need to check that this dbuf is not dirty in any future
* txg's (as we do in the normal dmu_sync() path). For simplicity, we
* don't nopwrite in this case.
*/
zp->zp_nopwrite = B_FALSE;
zio_nowait(zio_write(pio, os->os_spa, dmu_tx_get_txg(tx), zgd->zgd_bp,
abd_get_from_buf(zgd->zgd_db->db_data, zgd->zgd_db->db_size),
zgd->zgd_db->db_size, zgd->zgd_db->db_size, zp,
@ -1687,7 +1703,6 @@ dmu_sync_late_arrival(zio_t *pio, objset_t *os, dmu_sync_cb_t *done, zgd_t *zgd,
int
dmu_sync(zio_t *pio, uint64_t txg, dmu_sync_cb_t *done, zgd_t *zgd)
{
blkptr_t *bp = zgd->zgd_bp;
dmu_buf_impl_t *db = (dmu_buf_impl_t *)zgd->zgd_db;
objset_t *os = db->db_objset;
dsl_dataset_t *ds = os->os_dsl_dataset;
@ -1754,6 +1769,21 @@ dmu_sync(zio_t *pio, uint64_t txg, dmu_sync_cb_t *done, zgd_t *zgd)
ASSERT(dr->dr_next == NULL || dr->dr_next->dr_txg < txg);
if (db->db_blkptr != NULL) {
/*
* We need to fill in zgd_bp with the current blkptr so that
* the nopwrite code can check if we're writing the same
* data that's already on disk. We can only nopwrite if we
* are sure that after making the copy, db_blkptr will not
* change until our i/o completes. We ensure this by
* holding the db_mtx, and only allowing nopwrite if the
* block is not already dirty (see below). This is verified
* by dmu_sync_done(), which VERIFYs that the db_blkptr has
* not changed.
*/
*zgd->zgd_bp = *db->db_blkptr;
}
/*
* Assume the on-disk data is X, the current syncing data (in
* txg - 1) is Y, and the current in-memory data is Z (currently
@ -1805,7 +1835,7 @@ dmu_sync(zio_t *pio, uint64_t txg, dmu_sync_cb_t *done, zgd_t *zgd)
dsa->dsa_tx = NULL;
zio_nowait(arc_write(pio, os->os_spa, txg,
bp, dr->dt.dl.dr_data, DBUF_IS_L2CACHEABLE(db),
zgd->zgd_bp, dr->dt.dl.dr_data, DBUF_IS_L2CACHEABLE(db),
&zp, dmu_sync_ready, NULL, NULL, dmu_sync_done, dsa,
ZIO_PRIORITY_SYNC_WRITE, ZIO_FLAG_CANFAIL, &zb));

7
module/zfs/zfs_vnops.c
View File

@ -1002,7 +1002,6 @@ zfs_get_data(void *arg, lr_write_t *lr, char *buf, zio_t *zio)
uint64_t object = lr->lr_foid;
uint64_t offset = lr->lr_offset;
uint64_t size = lr->lr_length;
blkptr_t *bp = &lr->lr_blkptr;
dmu_buf_t *db;
zgd_t *zgd;
int error = 0;
@ -1079,11 +1078,7 @@ zfs_get_data(void *arg, lr_write_t *lr, char *buf, zio_t *zio)
DMU_READ_NO_PREFETCH);
if (error == 0) {
blkptr_t *obp = dmu_buf_get_blkptr(db);
if (obp) {
ASSERT(BP_IS_HOLE(bp));
*bp = *obp;
}
blkptr_t *bp = &lr->lr_blkptr;
zgd->zgd_db = db;
zgd->zgd_bp = bp;

10
module/zfs/zvol.c
View File

@ -36,6 +36,7 @@
*
* Copyright 2014 Nexenta Systems, Inc. All rights reserved.
* Copyright (c) 2016 Actifio, Inc. All rights reserved.
* Copyright (c) 2012, 2017 by Delphix. All rights reserved.
*/
/*
@ -1018,7 +1019,6 @@ zvol_get_data(void *arg, lr_write_t *lr, char *buf, zio_t *zio)
zvol_state_t *zv = arg;
uint64_t offset = lr->lr_offset;
uint64_t size = lr->lr_length;
blkptr_t *bp = &lr->lr_blkptr;
dmu_buf_t *db;
zgd_t *zgd;
int error;
@ -1047,14 +1047,10 @@ zvol_get_data(void *arg, lr_write_t *lr, char *buf, zio_t *zio)
error = dmu_buf_hold_by_dnode(zv->zv_dn, offset, zgd, &db,
DMU_READ_NO_PREFETCH);
if (error == 0) {
blkptr_t *obp = dmu_buf_get_blkptr(db);
if (obp) {
ASSERT(BP_IS_HOLE(bp));
*bp = *obp;
}
blkptr_t *bp = &lr->lr_blkptr;
zgd->zgd_db = db;
zgd->zgd_bp = &lr->lr_blkptr;
zgd->zgd_bp = bp;
ASSERT(db != NULL);
ASSERT(db->db_offset == offset);