ca84529a84
KCSAN complains about a data race when accessing the last_trans field of a root: [ 199.553628] BUG: KCSAN: data-race in btrfs_record_root_in_trans [btrfs] / record_root_in_trans [btrfs] [ 199.555186] read to 0x000000008801e308 of 8 bytes by task 2812 on cpu 1: [ 199.555210] btrfs_record_root_in_trans+0x9a/0x128 [btrfs] [ 199.555999] start_transaction+0x154/0xcd8 [btrfs] [ 199.556780] btrfs_join_transaction+0x44/0x60 [btrfs] [ 199.557559] btrfs_dirty_inode+0x9c/0x140 [btrfs] [ 199.558339] btrfs_update_time+0x8c/0xb0 [btrfs] [ 199.559123] touch_atime+0x16c/0x1e0 [ 199.559151] pipe_read+0x6a8/0x7d0 [ 199.559179] vfs_read+0x466/0x498 [ 199.559204] ksys_read+0x108/0x150 [ 199.559230] __s390x_sys_read+0x68/0x88 [ 199.559257] do_syscall+0x1c6/0x210 [ 199.559286] __do_syscall+0xc8/0xf0 [ 199.559318] system_call+0x70/0x98 [ 199.559431] write to 0x000000008801e308 of 8 bytes by task 2808 on cpu 0: [ 199.559464] record_root_in_trans+0x196/0x228 [btrfs] [ 199.560236] btrfs_record_root_in_trans+0xfe/0x128 [btrfs] [ 199.561097] start_transaction+0x154/0xcd8 [btrfs] [ 199.561927] btrfs_join_transaction+0x44/0x60 [btrfs] [ 199.562700] btrfs_dirty_inode+0x9c/0x140 [btrfs] [ 199.563493] btrfs_update_time+0x8c/0xb0 [btrfs] [ 199.564277] file_update_time+0xb8/0xf0 [ 199.564301] pipe_write+0x8ac/0xab8 [ 199.564326] vfs_write+0x33c/0x588 [ 199.564349] ksys_write+0x108/0x150 [ 199.564372] __s390x_sys_write+0x68/0x88 [ 199.564397] do_syscall+0x1c6/0x210 [ 199.564424] __do_syscall+0xc8/0xf0 [ 199.564452] system_call+0x70/0x98 This is because we update and read last_trans concurrently without any type of synchronization. This should be generally harmless and in the worst case it can make us do extra locking (btrfs_record_root_in_trans()) trigger some warnings at ctree.c or do extra work during relocation - this would probably only happen in case of load or store tearing. So fix this by always reading and updating the field using READ_ONCE() and WRITE_ONCE(), this silences KCSAN and prevents load and store tearing. Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.