block: fix handling of dead zone write plugs#830
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Shin'ichiro reported hard to reproduce unaligned write errors with zoned block devices. Under normal operation conditions (e.g. running XFS on an SMR disk), these errors are nearly impossible to trigger. But using a "slow" kernel with many debug options enables and some specific use cases (e.g. fio zbd test case 46), the errors can be reproduced fairly easily. The unaligned write errors come from mishandling a valid reference counting pattern of zone write plugs. Such pattern triggers for instance if a process A writes a zone (not necessarilly to the full state), another process B immediately resets the zone and immediately following the completion of the zone reset, starts issuing writes to the zone. With such pattern, in some cases, the zone write plugs worker thread of the device may still be holding a reference to the zone write plug of the zone taken when process A was writing to the zone. The following zone reset from process B marks the zone as dead but does not remove the zone write plug from the device hash table as a reference to the plug still exist. Once process B starts issuing new writes, the zone write plug is seen as dead and the writes from process B are immediately failed, despite this write pattern being perfectly legal. Fix this by allowing restoring a dead zone write plug to a live state if a write is issued to the zone when the zone is: marked as dead, empty and the write sector corresponds to the first sector of the zone (that is, the write is aligned to the zone write pointer). This is done with the new helper function disk_check_zone_wplug_dead(), which restores a dead zone write plug to a live state by clearing the BLK_ZONE_WPLUG_DEAD flag and restoring the initial reference to the zone write plug taken when the plug was added to the device hash table. Reported-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com> Fixes: b7d4ffb ("block: fix zone write plug removal") Signed-off-by: Damien Le Moal <dlemoal@kernel.org> Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
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Pull request for series with
subject: block: fix handling of dead zone write plugs
version: 1
url: https://patchwork.kernel.org/project/linux-block/list/?series=1094144