On Mon, Jan 27, 2020 at 10:01 AM Nikolay Borisov <nborisov@xxxxxxxx> wrote: > > Raviu reported that running his regular fs_trim segfaulted with the > following backtrace: > > [ 237.525947] assertion failed: prev, in ../fs/btrfs/extent_io.c:1595 > [ 237.525984] ------------[ cut here ]------------ > [ 237.525985] kernel BUG at ../fs/btrfs/ctree.h:3117! > [ 237.525992] invalid opcode: 0000 [#1] SMP PTI > [ 237.525998] CPU: 4 PID: 4423 Comm: fstrim Tainted: G U OE 5.4.14-8-vanilla #1 > [ 237.526001] Hardware name: ASUSTeK COMPUTER INC. > [ 237.526044] RIP: 0010:assfail.constprop.58+0x18/0x1a [btrfs] > [ 237.526079] Call Trace: > [ 237.526120] find_first_clear_extent_bit+0x13d/0x150 [btrfs] > [ 237.526148] btrfs_trim_fs+0x211/0x3f0 [btrfs] > [ 237.526184] btrfs_ioctl_fitrim+0x103/0x170 [btrfs] > [ 237.526219] btrfs_ioctl+0x129a/0x2ed0 [btrfs] > [ 237.526227] ? filemap_map_pages+0x190/0x3d0 > [ 237.526232] ? do_filp_open+0xaf/0x110 > [ 237.526238] ? _copy_to_user+0x22/0x30 > [ 237.526242] ? cp_new_stat+0x150/0x180 > [ 237.526247] ? do_vfs_ioctl+0xa4/0x640 > [ 237.526278] ? btrfs_ioctl_get_supported_features+0x30/0x30 [btrfs] > [ 237.526283] do_vfs_ioctl+0xa4/0x640 > [ 237.526288] ? __do_sys_newfstat+0x3c/0x60 > [ 237.526292] ksys_ioctl+0x70/0x80 > [ 237.526297] __x64_sys_ioctl+0x16/0x20 > [ 237.526303] do_syscall_64+0x5a/0x1c0 > [ 237.526310] entry_SYSCALL_64_after_hwframe+0x49/0xbe > > That was due to btrfs_fs_device::aloc_tree being empty. Initially I > thought this wasn't possible and as a percaution have put the assert in > find_first_clear_extent_bit. Turns out this is indeed possible and could > happen when a file system with SINGLE data/metadata profile has a 2nd > device added. Until balance is run or a new chunk is allocated on this > device it will be completely empty. > > In this case find_first_clear_extent_bit should return the full range > [0, -1ULL] and let the caller handle this i.e for trim the end will be > capped at the size of actual device. > > Link: https://lore.kernel.org/linux-btrfs/izW2WNyvy1dEDweBICizKnd2KDwDiDyY2EYQr4YCwk7pkuIpthx-JRn65MPBde00ND6V0_Lh8mW0kZwzDiLDv25pUYWxkskWNJnVP0kgdMA=@protonmail.com/ > Fixes: 45bfcfc168f8 ("btrfs: Implement find_first_clear_extent_bit") > Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx> > --- > > David can you try and squeeze this into 5.5? It only leads to an assertion > failure trigger (if assertion > fs/btrfs/extent_io.c | 32 ++++++++++++++++++-------------- > fs/btrfs/tests/extent-io-tests.c | 7 +++++++ > 2 files changed, 25 insertions(+), 14 deletions(-) > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > index 0351dbe64550..9bf7dffa22b1 100644 > --- a/fs/btrfs/extent_io.c > +++ b/fs/btrfs/extent_io.c > @@ -1593,21 +1593,25 @@ void find_first_clear_extent_bit(struct extent_io_tree *tree, u64 start, > /* Find first extent with bits cleared */ > while (1) { > node = __etree_search(tree, start, &next, &prev, NULL, NULL); > - if (!node) { > + if (!node && !next && !prev) { > + /* > + * Tree is completely empty, send full range and let > + * caller deal with it > + */ > + *start_ret = 0; > + *end_ret = -1; > + goto out; > + } else if (!node && !next) { > + /* > + * We are past the last allocated chunk, set start at > + * the end of the last extent. > + */ > + state = rb_entry(prev, struct extent_state, rb_node); > + *start_ret = state->end + 1; > + *end_ret = -1; > + goto out; > + } else if (!node) { > node = next; > - if (!node) { > - /* > - * We are past the last allocated chunk, > - * set start at the end of the last extent. The > - * device alloc tree should never be empty so > - * prev is always set. > - */ > - ASSERT(prev); > - state = rb_entry(prev, struct extent_state, rb_node); > - *start_ret = state->end + 1; > - *end_ret = -1; > - goto out; > - } > } > /* > * At this point 'node' either contains 'start' or start is > diff --git a/fs/btrfs/tests/extent-io-tests.c b/fs/btrfs/tests/extent-io-tests.c > index 123d9a614357..2708c7e620cb 100644 > --- a/fs/btrfs/tests/extent-io-tests.c > +++ b/fs/btrfs/tests/extent-io-tests.c > @@ -441,8 +441,15 @@ static int test_find_first_clear_extent_bit(void) > int ret = -EINVAL; > > test_msg("running find_first_clear_extent_bit test"); > + > extent_io_tree_init(NULL, &tree, IO_TREE_SELFTEST, NULL); > > + /* Test correct handling of empty tree */ > + find_first_clear_extent_bit(&tree, 0, &start, &end, CHUNK_TRIMMED); > + if (start != 0 || end != -1) { > + test_err("error getting a range from completely empty tree: start %llu end %llu", > + start, end); > + } Missing a 'goto out', otherwise the test doesn't fail. Thanks. > /* > * Set 1M-4M alloc/discard and 32M-64M thus leaving a hole between > * 4M-32M > -- > 2.17.1 > -- Filipe David Manana, “Whether you think you can, or you think you can't — you're right.”
