forked from Minki/linux
Btrfs: fix locking bugs when defragging leaves
When running fstests btrfs/070, with a higher number of fsstress operations, I ran frequently into two different locking bugs when defragging directories. The first bug produced the following traces: [133860.229792] ------------[ cut here ]------------ [133860.251062] WARNING: CPU: 2 PID: 26057 at fs/btrfs/locking.c:46 btrfs_set_lock_blocking_rw+0x57/0xbd [btrfs]() [133860.253576] Modules linked in: btrfs crc32c_generic xor raid6_pq nfsd auth_rpcgss oid_registry nfs_acl nfs lockd grace fscache sunrpc loop fuse parport_pc i2c_piix4 psmouse parport [133860.282566] CPU: 2 PID: 26057 Comm: btrfs Tainted: G W 4.3.0-rc5-btrfs-next-17+ #1 [133860.284393] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20150316_085822-nilsson.home.kraxel.org 04/01/2014 [133860.286827] 0000000000000000 ffff880207697b78 ffffffff812566f4 0000000000000000 [133860.288341] ffff880207697bb0 ffffffff8104d0a6 ffffffffa052d4c1 ffff880178f60e00 [133860.294219] ffff880178f60e00 0000000000000000 00000000000000f6 ffff880207697bc0 [133860.295831] Call Trace: [133860.306518] [<ffffffff812566f4>] dump_stack+0x4e/0x79 [133860.307473] [<ffffffff8104d0a6>] warn_slowpath_common+0x9f/0xb8 [133860.308619] [<ffffffffa052d4c1>] ? btrfs_set_lock_blocking_rw+0x57/0xbd [btrfs] [133860.310068] [<ffffffff8104d172>] warn_slowpath_null+0x1a/0x1c [133860.312552] [<ffffffffa052d4c1>] btrfs_set_lock_blocking_rw+0x57/0xbd [btrfs] [133860.314630] [<ffffffffa04d5787>] btrfs_set_lock_blocking+0xe/0x10 [btrfs] [133860.323596] [<ffffffffa04d99cb>] btrfs_realloc_node+0xb3/0x341 [btrfs] [133860.325233] [<ffffffffa050e396>] btrfs_defrag_leaves+0x239/0x2fa [btrfs] [133860.332427] [<ffffffffa04fc2ce>] btrfs_defrag_root+0x63/0xca [btrfs] [133860.337259] [<ffffffffa052a34e>] btrfs_ioctl_defrag+0x78/0x14e [btrfs] [133860.340147] [<ffffffffa052b00b>] btrfs_ioctl+0x746/0x24c6 [btrfs] [133860.344833] [<ffffffff81087481>] ? arch_local_irq_save+0x9/0xc [133860.346343] [<ffffffff8113ad61>] ? __might_fault+0x4c/0xa7 [133860.353248] [<ffffffff8113ad61>] ? __might_fault+0x4c/0xa7 [133860.354242] [<ffffffff8113adba>] ? __might_fault+0xa5/0xa7 [133860.355232] [<ffffffff81171139>] ? cp_new_stat+0x15d/0x174 [133860.356237] [<ffffffff8117c610>] do_vfs_ioctl+0x427/0x4e6 [133860.358587] [<ffffffff81171175>] ? SYSC_newfstat+0x25/0x2e [133860.360195] [<ffffffff8118574d>] ? __fget_light+0x4d/0x71 [133860.361380] [<ffffffff8117c726>] SyS_ioctl+0x57/0x79 [133860.363578] [<ffffffff8147cd97>] entry_SYSCALL_64_fastpath+0x12/0x6f [133860.366217] ---[ end trace 2cadb2f653437e49 ]--- [133860.367399] ------------[ cut here ]------------ [133860.368162] kernel BUG at fs/btrfs/locking.c:307! [133860.369430] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC [133860.370205] Modules linked in: btrfs crc32c_generic xor raid6_pq nfsd auth_rpcgss oid_registry nfs_acl nfs lockd grace fscache sunrpc loop fuse parport_pc i2c_piix4 psmouse parport [133860.370205] CPU: 2 PID: 26057 Comm: btrfs Tainted: G W 4.3.0-rc5-btrfs-next-17+ #1 [133860.370205] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20150316_085822-nilsson.home.kraxel.org 04/01/2014 [133860.370205] task: ffff8800aec6db40 ti: ffff880207694000 task.ti: ffff880207694000 [133860.370205] RIP: 0010:[<ffffffffa052d466>] [<ffffffffa052d466>] btrfs_assert_tree_locked+0x10/0x14 [btrfs] [133860.370205] RSP: 0018:ffff880207697bc0 EFLAGS: 00010246 [133860.370205] RAX: 0000000000000000 RBX: ffff880178f60e00 RCX: 0000000000000000 [133860.370205] RDX: ffff88023ec4fb50 RSI: 00000000ffffffff RDI: ffff880178f60e00 [133860.370205] RBP: ffff880207697bc0 R08: 0000000000000001 R09: 0000000000000000 [133860.370205] R10: 0000160000000000 R11: ffffffff81651000 R12: ffff880178f60e00 [133860.370205] R13: 0000000000000000 R14: 00000000000000f6 R15: ffff8801ff409000 [133860.370205] FS: 00007f763efd48c0(0000) GS:ffff88023ec40000(0000) knlGS:0000000000000000 [133860.370205] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [133860.370205] CR2: 0000000002158048 CR3: 000000003fd6c000 CR4: 00000000000006e0 [133860.370205] Stack: [133860.370205] ffff880207697bd8 ffffffffa052d4d0 0000000000000000 ffff880207697be8 [133860.370205] ffffffffa04d5787 ffff880207697c80 ffffffffa04d99cb ffff8801ff409590 [133860.370205] ffff880207697ca8 000000f507697c80 ffff880183c11bb8 0000000000000000 [133860.370205] Call Trace: [133860.370205] [<ffffffffa052d4d0>] btrfs_set_lock_blocking_rw+0x66/0xbd [btrfs] [133860.370205] [<ffffffffa04d5787>] btrfs_set_lock_blocking+0xe/0x10 [btrfs] [133860.370205] [<ffffffffa04d99cb>] btrfs_realloc_node+0xb3/0x341 [btrfs] [133860.370205] [<ffffffffa050e396>] btrfs_defrag_leaves+0x239/0x2fa [btrfs] [133860.370205] [<ffffffffa04fc2ce>] btrfs_defrag_root+0x63/0xca [btrfs] [133860.370205] [<ffffffffa052a34e>] btrfs_ioctl_defrag+0x78/0x14e [btrfs] [133860.370205] [<ffffffffa052b00b>] btrfs_ioctl+0x746/0x24c6 [btrfs] [133860.370205] [<ffffffff81087481>] ? arch_local_irq_save+0x9/0xc [133860.370205] [<ffffffff8113ad61>] ? __might_fault+0x4c/0xa7 [133860.370205] [<ffffffff8113ad61>] ? __might_fault+0x4c/0xa7 [133860.370205] [<ffffffff8113adba>] ? __might_fault+0xa5/0xa7 [133860.370205] [<ffffffff81171139>] ? cp_new_stat+0x15d/0x174 [133860.370205] [<ffffffff8117c610>] do_vfs_ioctl+0x427/0x4e6 [133860.370205] [<ffffffff81171175>] ? SYSC_newfstat+0x25/0x2e [133860.370205] [<ffffffff8118574d>] ? __fget_light+0x4d/0x71 [133860.370205] [<ffffffff8117c726>] SyS_ioctl+0x57/0x79 [133860.370205] [<ffffffff8147cd97>] entry_SYSCALL_64_fastpath+0x12/0x6f This bug happened because we assumed that by setting keep_locks to 1 in our search path, our path after a call to btrfs_search_slot() would have all nodes locked, which is not always true because unlock_up() (called by btrfs_search_slot()) will unlock a node in a path if the slot of the node below it doesn't point to the last item or beyond the last item. For example, when the tree has a heigth of 2 and path->slots[0] has a value smaller than btrfs_header_nritems(path->nodes[0]) - 1, the node at level 2 will be unlocked (also because lowest_unlock is set to 1 due to the fact that the value passed as ins_len to btrfs_search_slot is 0). This resulted in btrfs_find_next_key(), called before btrfs_realloc_node(), to release out path and call again btrfs_search_slot(), but this time with the cow parameter set to 0, meaning the resulting path got only read locks. Therefore when we called btrfs_realloc_node(), with path->nodes[1] having a read lock, it resulted in the warning and BUG_ON when calling btrfs_set_lock_blocking() against the node, as that function expects the node to have a write lock. The second bug happened often when the first bug didn't happen, and made us hang and hitting the following warning at fs/btrfs/locking.c: 251 void btrfs_tree_lock(struct extent_buffer *eb) 252 { 253 WARN_ON(eb->lock_owner == current->pid); This happened because the tree search we made at btrfs_defrag_leaves() before calling btrfs_find_next_key() locked a leaf and all the other nodes in the path, so btrfs_find_next_key() had no need to release the path and make a new search (with path->lowest_level set to 1). This made btrfs_realloc_node() attempt to write lock the same leaf again, resulting in a hang/deadlock. So fix these issues by calling btrfs_find_next_key() after calling btrfs_realloc_node() and setting the search path's lowest_level to 1 to avoid the hang/deadlock when attempting to write lock the leaves at btrfs_realloc_node(). Signed-off-by: Filipe Manana <fdmanana@suse.com>
This commit is contained in:
Filipe Manana
parent
f28a492878
commit
0376374a98
@ -89,6 +89,12 @@ int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
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goto out;
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}
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btrfs_release_path(path);
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/*
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* We don't need a lock on a leaf. btrfs_realloc_node() will lock all
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* leafs from path->nodes[1], so set lowest_level to 1 to avoid later
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* a deadlock (attempting to write lock an already write locked leaf).
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*/
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path->lowest_level = 1;
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wret = btrfs_search_slot(trans, root, &key, path, 0, 1);
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if (wret < 0) {
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@ -99,9 +105,12 @@ int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
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ret = 0;
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goto out;
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}
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path->slots[1] = btrfs_header_nritems(path->nodes[1]);
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next_key_ret = btrfs_find_next_key(root, path, &key, 1,
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min_trans);
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/*
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* The node at level 1 must always be locked when our path has
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* keep_locks set and lowest_level is 1, regardless of the value of
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* path->slots[1].
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*/
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BUG_ON(path->locks[1] == 0);
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ret = btrfs_realloc_node(trans, root,
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path->nodes[1], 0,
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&last_ret,
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@ -110,6 +119,18 @@ int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
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WARN_ON(ret == -EAGAIN);
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goto out;
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}
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/*
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* Now that we reallocated the node we can find the next key. Note that
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* btrfs_find_next_key() can release our path and do another search
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* without COWing, this is because even with path->keep_locks = 1,
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* btrfs_search_slot() / ctree.c:unlock_up() does not keeps a lock on a
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* node when path->slots[node_level - 1] does not point to the last
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* item or a slot beyond the last item (ctree.c:unlock_up()). Therefore
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* we search for the next key after reallocating our node.
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*/
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path->slots[1] = btrfs_header_nritems(path->nodes[1]);
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next_key_ret = btrfs_find_next_key(root, path, &key, 1,
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min_trans);
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if (next_key_ret == 0) {
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memcpy(&root->defrag_progress, &key, sizeof(key));
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ret = -EAGAIN;
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