While doing a ranged fsync, that is, one whose range doesn't cover the
whole possible file range (0 to LLONG_MAX), we can crash under certain
circumstances with a trace like the following:
[41074.641913] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC
(...)
[41074.642692] CPU: 0 PID: 24580 Comm: fsx Not tainted 3.16.0-fdm-btrfs-next-45+ #1
(...)
[41074.643886] RIP: 0010:[<ffffffffa01ecc99>] [<ffffffffa01ecc99>] btrfs_ordered_update_i_size+0x279/0x2b0 [btrfs]
(...)
[41074.644919] Stack:
(...)
[41074.644919] Call Trace:
[41074.644919] [<ffffffffa01db531>] btrfs_truncate_inode_items+0x3f1/0xa10 [btrfs]
[41074.644919] [<ffffffffa01eb54f>] ? btrfs_get_logged_extents+0x4f/0x80 [btrfs]
[41074.644919] [<ffffffffa02137a9>] btrfs_log_inode+0x2f9/0x970 [btrfs]
[41074.644919] [<ffffffff81090875>] ? sched_clock_local+0x25/0xa0
[41074.644919] [<ffffffff8164a55e>] ? mutex_unlock+0xe/0x10
[41074.644919] [<ffffffff810af51d>] ? trace_hardirqs_on+0xd/0x10
[41074.644919] [<ffffffffa0214b4f>] btrfs_log_inode_parent+0x1ef/0x560 [btrfs]
[41074.644919] [<ffffffff811d0c55>] ? dget_parent+0x5/0x180
[41074.644919] [<ffffffffa0215d11>] btrfs_log_dentry_safe+0x51/0x80 [btrfs]
[41074.644919] [<ffffffffa01e2d1a>] btrfs_sync_file+0x1ba/0x3e0 [btrfs]
[41074.644919] [<ffffffff811eda6b>] vfs_fsync_range+0x1b/0x30
(...)
The necessary conditions that lead to such crash are:
* an incremental fsync (when the inode doesn't have the
BTRFS_INODE_NEEDS_FULL_SYNC flag set) happened for our file and it logged
a file extent item ending at offset X;
* the file got the flag BTRFS_INODE_NEEDS_FULL_SYNC set in its inode, due
to a file truncate operation that reduces the file to a size smaller
than X;
* a ranged fsync call happens (via an msync for example), with a range that
doesn't cover the whole file and the end of this range, lets call it Y, is
smaller than X;
* btrfs_log_inode, sees the flag BTRFS_INODE_NEEDS_FULL_SYNC set and
calls btrfs_truncate_inode_items() to remove all items from the log
tree that are associated with our file;
* btrfs_truncate_inode_items() removes all of the inode's items, and the lowest
file extent item it removed is the one ending at offset X, where X > 0 and
X > Y - before returning, it calls btrfs_ordered_update_i_size() with an offset
parameter set to X;
* btrfs_ordered_update_i_size() sees that X is greater then the current ordered
size (btrfs_inode's disk_i_size) and then it assumes there can't be any ongoing
ordered operation with a range covering the offset X, calling a BUG_ON() if
such ordered operation exists. This assumption is made because the disk_i_size
is only increased after the corresponding file extent item is added to the
btree (btrfs_finish_ordered_io);
* But because our fsync covers only a limited range, such an ordered extent might
exist, and our fsync callback (btrfs_sync_file) doesn't wait for such ordered
extent to finish when calling btrfs_wait_ordered_range();
And then by the time btrfs_ordered_update_i_size() is called, via:
btrfs_sync_file() ->
btrfs_log_dentry_safe() ->
btrfs_log_inode_parent() ->
btrfs_log_inode() ->
btrfs_truncate_inode_items() ->
btrfs_ordered_update_i_size()
We hit the BUG_ON(), which could never happen if the fsync range covered the whole
possible file range (0 to LLONG_MAX), as we would wait for all ordered extents to
finish before calling btrfs_truncate_inode_items().
So just don't call btrfs_ordered_update_i_size() if we're removing the inode's items
from a log tree, which isn't supposed to change the in memory inode's disk_i_size.
Issue found while running xfstests/generic/127 (happens very rarely for me), more
specifically via the fsx calls that use memory mapped IO (and issue msync calls).
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
dac5705cad