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[PATCH 4.8 55/96] md/raid5: limit request size according to implementation limits

From Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Newsgroups linux.kernel
Subject [PATCH 4.8 55/96] md/raid5: limit request size according to implementation limits
Date 2017-01-07 00:10 +0100
Message-ID <sWLO3-sV-71@gated-at.bofh.it> (permalink)
References <sWKyC-7RC-5@gated-at.bofh.it>
Organization linux.* mail to news gateway

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4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

commit e8d7c33232e5fdfa761c3416539bc5b4acd12db5 upstream.

Current implementation employ 16bit counter of active stripes in lower
bits of bio->bi_phys_segments. If request is big enough to overflow
this counter bio will be completed and freed too early.

Fortunately this not happens in default configuration because several
other limits prevent that: stripe_cache_size * nr_disks effectively
limits count of active stripes. And small max_sectors_kb at lower
disks prevent that during normal read/write operations.

Overflow easily happens in discard if it's enabled by module parameter
"devices_handle_discard_safely" and stripe_cache_size is set big enough.

This patch limits requests size with 256Mb - 8Kb to prevent overflows.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Shaohua Li <shli@kernel.org>
Cc: Neil Brown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/raid5.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7017,6 +7017,15 @@ static int raid5_run(struct mddev *mddev
 			stripe = (stripe | (stripe-1)) + 1;
 		mddev->queue->limits.discard_alignment = stripe;
 		mddev->queue->limits.discard_granularity = stripe;
+
+		/*
+		 * We use 16-bit counter of active stripes in bi_phys_segments
+		 * (minus one for over-loaded initialization)
+		 */
+		blk_queue_max_hw_sectors(mddev->queue, 0xfffe * STRIPE_SECTORS);
+		blk_queue_max_discard_sectors(mddev->queue,
+					      0xfffe * STRIPE_SECTORS);
+
 		/*
 		 * unaligned part of discard request will be ignored, so can't
 		 * guarantee discard_zeroes_data

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[PATCH 4.8 00/96] 4.8.17-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-07 00:10 +0100
  [PATCH 4.8 17/96] hv: acquire vmbus_connection.channel_mutex in vmbus_free_channels() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-07 00:10 +0100
  [PATCH 4.8 52/96] s390/kexec: use node 0 when re-adding crash kernel memory Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-07 00:10 +0100
  [PATCH 4.8 26/96] drm/nouveau/ltc: protect clearing of comptags with mutex Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-07 00:10 +0100
  [PATCH 4.8 03/96] perf/x86: Fix exclusion of BTS and LBR for Goldmont Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-07 00:10 +0100
  [PATCH 4.8 53/96] arm64: KVM: pmu: Reset PMSELR_EL0.SEL to a sane value before entering the guest Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-07 00:10 +0100
  [PATCH 4.8 06/96] cfg80211/mac80211: fix BSS leaks when abandoning assoc attempts Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-07 00:10 +0100
  [PATCH 4.8 55/96] md/raid5: limit request size according to implementation limits Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-07 00:10 +0100
  Re: [PATCH 4.8 00/96] 4.8.17-stable review Shuah Khan <shuah.kh@samsung.com> - 2017-01-07 03:10 +0100
  Re: [PATCH 4.8 00/96] 4.8.17-stable review Guenter Roeck <linux@roeck-us.net> - 2017-01-07 17:00 +0100

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