RE: [PATCH RESEND] scsi_sysfs: protect against double execution of __scsi_remove_device()

From: KY Srinivasan
Date: Fri Nov 06 2015 - 12:48:15 EST

> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx]
> Sent: Friday, November 6, 2015 7:49 AM
> To: James E.J. Bottomley <JBottomley@xxxxxxxx>
> Cc: linux-scsi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; KY Srinivasan
> <kys@xxxxxxxxxxxxx>; Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
> Subject: [PATCH RESEND] scsi_sysfs: protect against double execution of
> __scsi_remove_device()
> On some host errors storvsc module tries to remove sdev by scheduling a job
> which does the following:
> sdev = scsi_device_lookup(wrk->host, 0, 0, wrk->lun);
> if (sdev) {
> scsi_remove_device(sdev);
> scsi_device_put(sdev);
> }
> While this code seems correct the following crash is observed:
> general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC
> RIP: 0010:[<ffffffff81169979>] [<ffffffff81169979>] bdi_destroy+0x39/0x220
> ...
> [<ffffffff814aecdc>] ? _raw_spin_unlock_irq+0x2c/0x40
> [<ffffffff8127b7db>] blk_cleanup_queue+0x17b/0x270
> [<ffffffffa00b54c4>] __scsi_remove_device+0x54/0xd0 [scsi_mod]
> [<ffffffffa00b556b>] scsi_remove_device+0x2b/0x40 [scsi_mod]
> [<ffffffffa00ec47d>] storvsc_remove_lun+0x3d/0x60 [hv_storvsc]
> [<ffffffff81080791>] process_one_work+0x1b1/0x530
> ...
> The problem comes with the fact that many such jobs (for the same device)
> are being scheduled simultaneously. While scsi_remove_device() uses
> shost->scan_mutex and scsi_device_lookup() will fail for a device in
> SDEV_DEL state there is no protection against someone who did
> scsi_device_lookup() before we actually entered __scsi_remove_device().
> So
> the whole scenario looks like that: two callers do simultaneous (or
> preemption happens) calls to scsi_device_lookup() ant these calls succeed
> for both of them, after that they try doing scsi_remove_device().
> shost->scan_mutex only serializes their calls to __scsi_remove_device()
> and we end up doing the cleanup path twice.
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>


I too have a bunch of patches in your queue (sent about a month ago).
Should I resend them as well.


K. Y
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