Hi all, There is a risk of data loss with md/raid6 arrays running on Linux since 2.6.32. If: - the array is doubly degraded - one or both failed devices are being recovered, and - the array is written to then it is possible for data on the array to be lost. The patch below fixes the problem. If you apply the patch to an older kernel which has separate handle_stripe5() and handle_stripe6() functions, be sure that patch changes handle_stripe6(). There is no risk to an optimal array or a singly-degraded array. There is also no risk on a doubly-degraded array which is not recovering a device or is not receiving write requests. If you have data on a RAID6 array, please consider how to avoid corruption, possibly by applying the patch, possibly by removing any hot spares so recovery does not automatically start. This patch will be sent upstream shortly and will subsequently appear in future "-stable" kernels. NeilBrown From f94e37dce722ec7b6666fd04be357f422daa02b5 Mon Sep 17 00:00:00 2001 From: NeilBrown <neilb@xxxxxxx> Date: Wed, 13 Aug 2014 09:57:07 +1000 Subject: [PATCH] md/raid6: avoid data corruption during recovery of double-degraded RAID6 During recovery of a double-degraded RAID6 it is possible for some blocks not to be recovered properly, leading to corruption. If a write happens to one block in a stripe that would be written to a missing device, and at the same time that stripe is recovering data to the other missing device, then that recovered data may not be written. This patch skips, in the double-degraded case, an optimisation that is only safe for single-degraded arrays. Bug was introduced in 2.6.32 and fix is suitable for any kernel since then. In an older kernel with separate handle_stripe5() and handle_stripe6() functions that patch must change handle_stripe6(). Cc: stable@xxxxxxxxxxxxxxx (2.6.32+) Fixes: 6c0069c0ae9659e3a91b68eaed06a5c6c37f45c8 Cc: Yuri Tikhonov <yur@xxxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Reported-by: "Manibalan P" <pmanibalan@xxxxxxxxxxxxxx> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1090423 Signed-off-by: NeilBrown <neilb@xxxxxxx> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index 6b2d615d1094..183588b11fc1 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -3817,6 +3817,8 @@ static void handle_stripe(struct stripe_head *sh) set_bit(R5_Wantwrite, &dev->flags); if (prexor) continue; + if (s.failed > 1) + continue; if (!test_bit(R5_Insync, &dev->flags) || ((i == sh->pd_idx || i == sh->qd_idx) && s.failed == 0))
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