This is a note to let you know that I've just added the patch titled md/raid5: preserve STRIPE_PREREAD_ACTIVE in break_stripe_batch_list to the 4.5-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: md-raid5-preserve-stripe_preread_active-in-break_stripe_batch_list.patch and it can be found in the queue-4.5 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 550da24f8d62fe81f3c13e3ec27602d6e44d43dc Mon Sep 17 00:00:00 2001 From: NeilBrown <neilb@xxxxxxxx> Date: Wed, 9 Mar 2016 12:58:25 +1100 Subject: md/raid5: preserve STRIPE_PREREAD_ACTIVE in break_stripe_batch_list From: NeilBrown <neilb@xxxxxxxx> commit 550da24f8d62fe81f3c13e3ec27602d6e44d43dc upstream. break_stripe_batch_list breaks up a batch and copies some flags from the batch head to the members, preserving others. It doesn't preserve or copy STRIPE_PREREAD_ACTIVE. This is not normally a problem as STRIPE_PREREAD_ACTIVE is cleared when a stripe_head is added to a batch, and is not set on stripe_heads already in a batch. However there is no locking to ensure one thread doesn't set the flag after it has just been cleared in another. This does occasionally happen. md/raid5 maintains a count of the number of stripe_heads with STRIPE_PREREAD_ACTIVE set: conf->preread_active_stripes. When break_stripe_batch_list clears STRIPE_PREREAD_ACTIVE inadvertently this could becomes incorrect and will never again return to zero. md/raid5 delays the handling of some stripe_heads until preread_active_stripes becomes zero. So when the above mention race happens, those stripe_heads become blocked and never progress, resulting is write to the array handing. So: change break_stripe_batch_list to preserve STRIPE_PREREAD_ACTIVE in the members of a batch. URL: https://bugzilla.kernel.org/show_bug.cgi?id=108741 URL: https://bugzilla.redhat.com/show_bug.cgi?id=1258153 URL: http://thread.gmane.org/5649C0E9.2030204@xxxxxxxx Reported-by: Martin Svec <martin.svec@xxxxxxxx> (and others) Tested-by: Tom Weber <linux@xxxxxxxxxxxxxxxx> Fixes: 1b956f7a8f9a ("md/raid5: be more selective about distributing flags across batch.") Signed-off-by: NeilBrown <neilb@xxxxxxxx> Signed-off-by: Shaohua Li <shli@xxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/md/raid5.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -4239,7 +4239,6 @@ static void break_stripe_batch_list(stru WARN_ON_ONCE(sh->state & ((1 << STRIPE_ACTIVE) | (1 << STRIPE_SYNCING) | (1 << STRIPE_REPLACED) | - (1 << STRIPE_PREREAD_ACTIVE) | (1 << STRIPE_DELAYED) | (1 << STRIPE_BIT_DELAY) | (1 << STRIPE_FULL_WRITE) | @@ -4254,6 +4253,7 @@ static void break_stripe_batch_list(stru (1 << STRIPE_REPLACED))); set_mask_bits(&sh->state, ~(STRIPE_EXPAND_SYNC_FLAGS | + (1 << STRIPE_PREREAD_ACTIVE) | (1 << STRIPE_DEGRADED)), head_sh->state & (1 << STRIPE_INSYNC)); Patches currently in stable-queue which might be from neilb@xxxxxxxx are queue-4.5/raid5-check_reshape-shouldn-t-call-mddev_suspend.patch queue-4.5/md-raid5-preserve-stripe_preread_active-in-break_stripe_batch_list.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html