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Lars Ellenberg d1ef3aed4d drbd: fix "LOGIC BUG" in drbd_al_begin_io_nonblock() 
commit ab140365fb upstream.

Even though we check that we "should" be able to do lc_get_cumulative()
while holding the device->al_lock spinlock, it may still fail,
if some other code path decided to do lc_try_lock() with bad timing.

If that happened, we logged "LOGIC BUG for enr=...",
but still did not return an error.

The rest of the code now assumed that this request has references
for the relevant activity log extents.

The implcations are that during an active resync, mutual exclusivity of
resync versus application IO is not guaranteed. And a potential crash
at this point may not realizs that these extents could have been target
of in-flight IO and would need to be resynced just in case.

Also, once the request completes, it will give up activity log references it
does not even hold, which will trigger a BUG_ON(refcnt == 0) in lc_put().

Fix:

Do not crash the kernel for a condition that is harmless during normal
operation: also catch "e->refcnt == 0", not only "e == NULL"
when being noisy about "al_complete_io() called on inactive extent %u\n".

And do not try to be smart and "guess" whether something will work, then
be surprised when it does not.
Deal with the fact that it may or may not work.  If it does not, remember a
possible "partially in activity log" state (only possible for requests that
cross extent boundaries), and return an error code from
drbd_al_begin_io_nonblock().

A latter call for the same request will then resume from where we left off.

Cc: stable@vger.kernel.org
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2026-03-12 07:09:42 -04:00
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README

README 

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.