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context: workaround to prevent LOGICAL_INO and btrfs balance from running concurrently

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This avoids some kernel bugs.  One of them is fixed in 5.3.4 and later:

	efad8a853a "Btrfs: fix use-after-free when using the tree modification log"

There are apparently others in current kernels, so for now just put bees
on pause until the balance is done.

At some point we may want to provide an option to disable this
workaround; however, running bees and balance at the same time makes
neither particularly fast, so maybe we'll just leave it this way.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell
2019-11-19 16:01:31 -05:00
committed by Kai Krakow
parent 6e75857d71
commit ac53e50d3e
2 changed files with 35 additions and 0 deletions
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31
src/bees-context.cc
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@@ -773,11 +773,42 @@ BeesResolveAddrResult::BeesResolveAddrResult()
{
}
void
BeesContext::wait_for_balance()
{
Timer balance_timer;
BEESNOTE("WORKAROUND: waiting for balance to stop");
while (true) {
btrfs_ioctl_balance_args args;
memset_zero<btrfs_ioctl_balance_args>(&args);
const int ret = ioctl(root_fd(), BTRFS_IOC_BALANCE_PROGRESS, &args);
if (ret < 0) {
// Either can't get balance status or not running, exit either way
break;
}
if (!(args.state & BTRFS_BALANCE_STATE_RUNNING)) {
// Balance not running, doesn't matter if paused or cancelled
break;
}
BEESLOGDEBUG("WORKAROUND: Waiting " << balance_timer << "s for balance to stop");
sleep(BEES_BALANCE_POLL_INTERVAL);
}
}
BeesResolveAddrResult
BeesContext::resolve_addr_uncached(BeesAddress addr)
{
THROW_CHECK1(invalid_argument, addr, !addr.is_magic());
THROW_CHECK0(invalid_argument, !!root_fd());
// Is there a bug where resolve and balance cause a crash (BUG_ON at fs/btrfs/ctree.c:1227)?
// Apparently yes, and more than one.
// Wait for the balance to finish before we run LOGICAL_INO
wait_for_balance();
// Time how long this takes
Timer resolve_timer;
// There is no performance benefit if we restrict the buffer size.