forked from Minki/linux
mainlining shenanigans
d189dd70e2
The device replace cancel thread can race with the replace start thread
and if fs_info::scrubs_running is not yet set, btrfs_scrub_cancel() will
fail to stop the scrub thread.
The scrub thread continues with the scrub for replace which then will
try to write to the target device and which is already freed by the
cancel thread.
scrub_setup_ctx() warns as tgtdev is NULL.
struct scrub_ctx *scrub_setup_ctx(struct btrfs_device *dev, int is_dev_replace)
{
...
if (is_dev_replace) {
WARN_ON(!fs_info->dev_replace.tgtdev); <===
sctx->pages_per_wr_bio = SCRUB_PAGES_PER_WR_BIO;
sctx->wr_tgtdev = fs_info->dev_replace.tgtdev;
sctx->flush_all_writes = false;
}
[ 6724.497655] BTRFS info (device sdb): dev_replace from /dev/sdb (devid 1) to /dev/sdc started
[ 6753.945017] BTRFS info (device sdb): dev_replace from /dev/sdb (devid 1) to /dev/sdc canceled
[ 6852.426700] WARNING: CPU: 0 PID: 4494 at fs/btrfs/scrub.c:622 scrub_setup_ctx.isra.19+0x220/0x230 [btrfs]
...
[ 6852.428928] RIP: 0010:scrub_setup_ctx.isra.19+0x220/0x230 [btrfs]
...
[ 6852.432970] Call Trace:
[ 6852.433202] btrfs_scrub_dev+0x19b/0x5c0 [btrfs]
[ 6852.433471] btrfs_dev_replace_start+0x48c/0x6a0 [btrfs]
[ 6852.433800] btrfs_dev_replace_by_ioctl+0x3a/0x60 [btrfs]
[ 6852.434097] btrfs_ioctl+0x2476/0x2d20 [btrfs]
[ 6852.434365] ? do_sigaction+0x7d/0x1e0
[ 6852.434623] do_vfs_ioctl+0xa9/0x6c0
[ 6852.434865] ? syscall_trace_enter+0x1c8/0x310
[ 6852.435124] ? syscall_trace_enter+0x1c8/0x310
[ 6852.435387] ksys_ioctl+0x60/0x90
[ 6852.435663] __x64_sys_ioctl+0x16/0x20
[ 6852.435907] do_syscall_64+0x50/0x180
[ 6852.436150] entry_SYSCALL_64_after_hwframe+0x49/0xbe
Further, as the replace thread enters scrub_write_page_to_dev_replace()
without the target device it panics:
static int scrub_add_page_to_wr_bio(struct scrub_ctx *sctx,
struct scrub_page *spage)
{
...
bio_set_dev(bio, sbio->dev->bdev); <======
[ 6929.715145] BUG: unable to handle kernel NULL pointer dereference at 00000000000000a0
..
[ 6929.717106] Workqueue: btrfs-scrub btrfs_scrub_helper [btrfs]
[ 6929.717420] RIP: 0010:scrub_write_page_to_dev_replace+0xb4/0x260
[btrfs]
..
[ 6929.721430] Call Trace:
[ 6929.721663] scrub_write_block_to_dev_replace+0x3f/0x60 [btrfs]
[ 6929.721975] scrub_bio_end_io_worker+0x1af/0x490 [btrfs]
[ 6929.722277] normal_work_helper+0xf0/0x4c0 [btrfs]
[ 6929.722552] process_one_work+0x1f4/0x520
[ 6929.722805] ? process_one_work+0x16e/0x520
[ 6929.723063] worker_thread+0x46/0x3d0
[ 6929.723313] kthread+0xf8/0x130
[ 6929.723544] ? process_one_work+0x520/0x520
[ 6929.723800] ? kthread_delayed_work_timer_fn+0x80/0x80
[ 6929.724081] ret_from_fork+0x3a/0x50
Fix this by letting the btrfs_dev_replace_finishing() to do the job of
cleaning after the cancel, including freeing of the target device.
btrfs_dev_replace_finishing() is called when btrfs_scub_dev() returns
along with the scrub return status.
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@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 Restructured Text 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.