From 2054f35e564b59e23950ee573e91dbae3fd2ccd9 Mon Sep 17 00:00:00 2001 From: George Amanakis Date: Fri, 10 Jul 2020 17:10:03 -0400 Subject: [PATCH] Fix a persistent L2ARC bug in l2arc_write_done() In case l2arc_write_done() handles a zio that was not successful check that the list of log block pointers is not empty when restoring them in the device header. Otherwise zero them out. In any case perform the actual write updating the device header after the zio of l2arc_write_buffers() completes as l2arc_write_done() may have touched the memory holding the log block pointers in the device header. Reviewed-by: Serapheim Dimitropoulos Reviewed-by: Brian Behlendorf Signed-off-by: George Amanakis Closes #10540 Closes #10543 --- module/zfs/arc.c | 32 +++++++++++++++++++++++++++----- 1 file changed, 27 insertions(+), 5 deletions(-) diff --git a/module/zfs/arc.c b/module/zfs/arc.c index 2048df4674..ea22686ccd 100644 --- a/module/zfs/arc.c +++ b/module/zfs/arc.c @@ -8018,9 +8018,27 @@ top: list_destroy(&cb->l2wcb_abd_list); if (zio->io_error != 0) { - /* restore the lbps array in the header to its previous state */ + /* + * Restore the lbps array in the header to its previous state. + * If the list of log block pointers is empty, zero out the + * log block pointers in the device header. + */ lb_ptr_buf = list_head(&dev->l2ad_lbptr_list); for (int i = 0; i < 2; i++) { + if (lb_ptr_buf == NULL) { + /* + * If the list is empty zero out the device + * header. Otherwise zero out the second log + * block pointer in the header. + */ + if (i == 0) { + bzero(l2dhdr, dev->l2ad_dev_hdr_asize); + } else { + bzero(&l2dhdr->dh_start_lbps[i], + sizeof (l2arc_log_blkptr_t)); + } + break; + } bcopy(lb_ptr_buf->lb_ptr, &l2dhdr->dh_start_lbps[i], sizeof (l2arc_log_blkptr_t)); lb_ptr_buf = list_next(&dev->l2ad_lbptr_list, @@ -8949,12 +8967,17 @@ l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz) ARCSTAT_INCR(arcstat_l2_lsize, write_lsize); ARCSTAT_INCR(arcstat_l2_psize, write_psize); - l2arc_dev_hdr_update(dev); - dev->l2ad_writing = B_TRUE; (void) zio_wait(pio); dev->l2ad_writing = B_FALSE; + /* + * Update the device header after the zio completes as + * l2arc_write_done() may have updated the memory holding the log block + * pointers in the device header. + */ + l2arc_dev_hdr_update(dev); + return (write_asize); } @@ -9970,8 +9993,7 @@ l2arc_log_blk_fetch_abort(zio_t *zio) } /* - * Creates a zio to update the device header on an l2arc device. The zio is - * initiated as a child of `pio'. + * Creates a zio to update the device header on an l2arc device. */ void l2arc_dev_hdr_update(l2arc_dev_t *dev)