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Storage devices which report supporting discard commands like WRITE_SAME_16 with unmap, but reject discard commands sent to the storage device. This is a clear storage firmware bug but it doesn't change the fact that should a program cause discards to be sent to a multipath device layered on this buggy storage, all paths can end up failed at the same time from the discards, causing possible I/O loss. The first discard to a path will fail with Illegal Request, Invalid field in cdb, e.g.: kernel: sd 8:0:8:19: [sdfn] tag#0 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE kernel: sd 8:0:8:19: [sdfn] tag#0 Sense Key : Illegal Request [current] kernel: sd 8:0:8:19: [sdfn] tag#0 Add. Sense: Invalid field in cdb kernel: sd 8:0:8:19: [sdfn] tag#0 CDB: Write same(16) 93 08 00 00 00 00 00 a0 08 00 00 00 80 00 00 00 kernel: blk_update_request: critical target error, dev sdfn, sector 10487808 The SCSI layer converts this to the BLK_STS_TARGET error number, the sd device disables its support for discard on this path, and because of the BLK_STS_TARGET error multipath fails the discard without failing any path or retrying down a different path. But subsequent discards can cause path failures. Any discards sent to the path which already failed a discard ends up failing with EIO from blk_cloned_rq_check_limits with an "over max size limit" error since the discard limit was set to 0 by the sd driver for the path. As the error is EIO, this now fails the path and multipath tries to send the discard down the next path. This cycle continues as discards are sent until all paths fail. Fix this by training DM core to disable DISCARD if the underlying storage already did so. Also, fix branching in dm_done() and clone_endio() to reflect the mutually exclussive nature of the IO operations in question. Cc: stable@vger.kernel.org Reported-by: David Jeffery <djeffery@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.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.