From c2e39305299f0118298c2201f6d6cc7d3485f29e Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Wed, 24 Nov 2021 14:14:23 -0500 Subject: btrfs: clear extent buffer uptodate when we fail to write it I got dmesg errors on generic/281 on our overnight fstests. Looking at the history this happens occasionally, with errors like this WARNING: CPU: 0 PID: 673217 at fs/btrfs/extent_io.c:6848 assert_eb_page_uptodate+0x3f/0x50 CPU: 0 PID: 673217 Comm: kworker/u4:13 Tainted: G W 5.16.0-rc2+ #469 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014 Workqueue: btrfs-cache btrfs_work_helper RIP: 0010:assert_eb_page_uptodate+0x3f/0x50 RSP: 0018:ffffae598230bc60 EFLAGS: 00010246 RAX: 0017ffffc0002112 RBX: ffffebaec4100900 RCX: 0000000000001000 RDX: ffffebaec45733c7 RSI: ffffebaec4100900 RDI: ffff9fd98919f340 RBP: 0000000000000d56 R08: ffff9fd98e300000 R09: 0000000000000000 R10: 0001207370a91c50 R11: 0000000000000000 R12: 00000000000007b0 R13: ffff9fd98919f340 R14: 0000000001500000 R15: 0000000001cb0000 FS: 0000000000000000(0000) GS:ffff9fd9fbc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f549fcf8940 CR3: 0000000114908004 CR4: 0000000000370ef0 Call Trace: extent_buffer_test_bit+0x3f/0x70 free_space_test_bit+0xa6/0xc0 load_free_space_tree+0x1d6/0x430 caching_thread+0x454/0x630 ? rcu_read_lock_sched_held+0x12/0x60 ? rcu_read_lock_sched_held+0x12/0x60 ? rcu_read_lock_sched_held+0x12/0x60 ? lock_release+0x1f0/0x2d0 btrfs_work_helper+0xf2/0x3e0 ? lock_release+0x1f0/0x2d0 ? finish_task_switch.isra.0+0xf9/0x3a0 process_one_work+0x270/0x5a0 worker_thread+0x55/0x3c0 ? process_one_work+0x5a0/0x5a0 kthread+0x174/0x1a0 ? set_kthread_struct+0x40/0x40 ret_from_fork+0x1f/0x30 This happens because we're trying to read from a extent buffer page that is !PageUptodate. This happens because we will clear the page uptodate when we have an IO error, but we don't clear the extent buffer uptodate. If we do a read later and find this extent buffer we'll think its valid and not return an error, and then trip over this warning. Fix this by also clearing uptodate on the extent buffer when this happens, so that we get an error when we do a btrfs_search_slot() and find this block later. CC: stable@vger.kernel.org # 5.4+ Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/extent_io.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'fs/btrfs/extent_io.c') diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 4e03a6d3aa32..dcdb97d9205d 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -4313,6 +4313,12 @@ static void set_btree_ioerr(struct page *page, struct extent_buffer *eb) if (test_and_set_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)) return; + /* + * A read may stumble upon this buffer later, make sure that it gets an + * error and knows there was an error. + */ + clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags); + /* * If we error out, we should add back the dirty_metadata_bytes * to make it consistent. -- cgit v1.2.3 From 68b85589ba8114514d83ae87dd6f3fe9b315cae0 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Wed, 24 Nov 2021 14:14:25 -0500 Subject: btrfs: call mapping_set_error() on btree inode with a write error generic/484 fails sometimes with compression on because the write ends up small enough that it goes into the btree. This means that we never call mapping_set_error() on the inode itself, because the page gets marked as fine when we inline it into the metadata. When the metadata writeback happens we see it and abort the transaction properly and mark the fs as readonly, however we don't do the mapping_set_error() on anything. In syncfs() we will simply return 0 if the sb is marked read-only, so we can't check for this in our syncfs callback. The only way the error gets returned if we called mapping_set_error() on something. Fix this by calling mapping_set_error() on the btree inode mapping. This allows us to properly return an error on syncfs and pass generic/484 with compression on. Reviewed-by: Nikolay Borisov Signed-off-by: Josef Bacik Signed-off-by: David Sterba --- fs/btrfs/extent_io.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'fs/btrfs/extent_io.c') diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index dcdb97d9205d..3258b6f01e85 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -4319,6 +4319,14 @@ static void set_btree_ioerr(struct page *page, struct extent_buffer *eb) */ clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags); + /* + * We need to set the mapping with the io error as well because a write + * error will flip the file system readonly, and then syncfs() will + * return a 0 because we are readonly if we don't modify the err seq for + * the superblock. + */ + mapping_set_error(page->mapping, -EIO); + /* * If we error out, we should add back the dirty_metadata_bytes * to make it consistent. -- cgit v1.2.3 From 651740a502411793327e2f0741104749c4eedcd1 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Mon, 13 Dec 2021 14:22:33 -0500 Subject: btrfs: check WRITE_ERR when trying to read an extent buffer Filipe reported a hang when we have errors on btrfs. This turned out to be a side-effect of my fix c2e39305299f01 ("btrfs: clear extent buffer uptodate when we fail to write it") which made it so we clear EXTENT_BUFFER_UPTODATE on an eb when we fail to write it out. Below is a paste of Filipe's analysis he got from using drgn to debug the hang """ btree readahead code calls read_extent_buffer_pages(), sets ->io_pages to a value while writeback of all pages has not yet completed: --> writeback for the first 3 pages finishes, we clear EXTENT_BUFFER_UPTODATE from eb on the first page when we get an error. --> at this point eb->io_pages is 1 and we cleared Uptodate bit from the first 3 pages --> read_extent_buffer_pages() does not see EXTENT_BUFFER_UPTODATE() so it continues, it's able to lock the pages since we obviously don't hold the pages locked during writeback --> read_extent_buffer_pages() then computes 'num_reads' as 3, and sets eb->io_pages to 3, since only the first page does not have Uptodate bit set at this point --> writeback for the remaining page completes, we ended decrementing eb->io_pages by 1, resulting in eb->io_pages == 2, and therefore never calling end_extent_buffer_writeback(), so EXTENT_BUFFER_WRITEBACK remains in the eb's flags --> of course, when the read bio completes, it doesn't and shouldn't call end_extent_buffer_writeback() --> we should clear EXTENT_BUFFER_UPTODATE only after all pages of the eb finished writeback? or maybe make the read pages code wait for writeback of all pages of the eb to complete before checking which pages need to be read, touch ->io_pages, submit read bio, etc writeback bit never cleared means we can hang when aborting a transaction, at: btrfs_cleanup_one_transaction() btrfs_destroy_marked_extents() wait_on_extent_buffer_writeback() """ This is a problem because our writes are not synchronized with reads in any way. We clear the UPTODATE flag and then we can easily come in and try to read the EB while we're still waiting on other bio's to complete. We have two options here, we could lock all the pages, and then check to see if eb->io_pages != 0 to know if we've already got an outstanding write on the eb. Or we can simply check to see if we have WRITE_ERR set on this extent buffer. We set this bit _before_ we clear UPTODATE, so if the read gets triggered because we aren't UPTODATE because of a write error we're guaranteed to have WRITE_ERR set, and in this case we can simply return -EIO. This will fix the reported hang. Reported-by: Filipe Manana Fixes: c2e39305299f01 ("btrfs: clear extent buffer uptodate when we fail to write it") CC: stable@vger.kernel.org # 5.4+ Reviewed-by: Filipe Manana Signed-off-by: Josef Bacik Signed-off-by: David Sterba --- fs/btrfs/extent_io.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'fs/btrfs/extent_io.c') diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 3258b6f01e85..9234d96a7fd5 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -6611,6 +6611,14 @@ int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num) if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags)) return 0; + /* + * We could have had EXTENT_BUFFER_UPTODATE cleared by the write + * operation, which could potentially still be in flight. In this case + * we simply want to return an error. + */ + if (unlikely(test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags))) + return -EIO; + if (eb->fs_info->sectorsize < PAGE_SIZE) return read_extent_buffer_subpage(eb, wait, mirror_num); -- cgit v1.2.3