Re: [PATCH scsi-misc-2.6 01/04] scsi: make scsi_send_eh_cmnd useits own timer instead of scmd->eh_timeout
From: James Bottomley
Date: Sun Apr 24 2005 - 18:28:11 EST
On Tue, 2005-04-19 at 23:31 +0900, Tejun Heo wrote:
> scmd->eh_timeout is used to resolve the race between command
> completion and timeout. However, during error handling,
> scsi_send_eh_cmnd uses scmd->eh_timeout. This creates a race
> condition between eh and normal completion for a request which
> has timed out and in the process of error handling. If the
> request completes while scmd->eh_timeout is being used by eh,
> eh timeout is lost and the command will be handled by both eh
> and completion path. This patch fixes the race by making
> scsi_send_eh_cmnd() use its own timer.
> This patch adds shost->eh_timeout field. The name of the
> field equals scmd->eh_timeout which is used for normal command
> timeout. As this can be confusing, renaming scmd->eh_timeout
> to something like scmd->cmd_timeout would be good.
> Reworked such that timeout race window is kept at minimal
> level as pointed out by James Bottomley.
This looks fine in principle. However, three comments
1. If you're doing this, there's no further use for eh_timeout, so
remove it (and preferably fix gdth_proc.c; however, it's better to break
the compile of that driver than have it rely on a now defunct field).
2. Use of eh_action is private to scsi_error.c, so you don't need to add
a new field to the host, just make eh_action a pointer to a private
eh_action structure which contains the timer and the semaphore.
3. To close a really tiny window where the running timer could race with
the del_timer, it should probably be del_timer_sync(). The practical
effect of this is nil, but it would be correct programming.
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