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Message-ID: <Pine.LNX.4.44L0.0803111352450.21625-100000@iolanthe.rowland.org>
Date: Tue, 11 Mar 2008 14:07:15 -0400 (EDT)
From: Alan Stern <stern@...land.harvard.edu>
To: Boaz Harrosh <bharrosh@...asas.com>
cc: James Bottomley <James.Bottomley@...senPartnership.com>,
Matthew Dharm <mdharm-usb@...-eyed-alien.net>,
Sven Schnelle <svens@...ckframe.org>,
<linux-kernel@...r.kernel.org>,
linux-scsi <linux-scsi@...r.kernel.org>,
FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] [SCSI] gdth: Allocate sense_buffer to prevent NULL
pointer dereference
On Tue, 11 Mar 2008, Boaz Harrosh wrote:
> I would like to fix this better by calling scsi_get/put_command but there is
> something fundamental that bothers me with isd200 driver. I can see that
> an isd200_info struct is allocated and put on a struct us_data->extra. But
> as I understand the code, the struct us_data is associated with a scsi_host
> not a scsi_device. Are we guarantied that we have only one scsi_device
> per host at all times?
>
> If not than the resources in isd200_info that are related to a request_queue
> and are used from a .queuecommand code-path are not thread safe. (Like the
> srb member)
>
> If Yes, then where in the code initialization sequence is the earliest place I
> can get to a scsi_device. I could do that on first call to .queuecommand but
> I would rather do it in a place that I could use GFP_KERNEL for allocation
> of the extra command? (Same question on the tear down of the scsi_device)
You can first get to the scsi_device in isd200_ata_command(). The last
place you can get to the scsi_device (if one exists!) is
quiesce_and_remove_host() -- but that's part of the core, not specific
to isd200.
> (And one more stupid question. Why does isd200_init_info allocates the info
> structure but the isd200_free_info_ptrs does not free it, it kind of
> limits the way it can be allocated, no?)
Not at all. isd200_free_info_ptrs() frees everything pointed to by the
info structure, and the info structure itself is freed later on by the
usb-storage core in usb_stor_release_resources().
If you wanted to free it in isd200_free_info_ptrs() you could; just
make sure to set us->extra to NULL when you do, to avoid a double-free
error.
Alan Stern
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