From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vitaly Kuznetsov Subject: [PATCH] scsi_sysfs: protect against double execution of __scsi_remove_device() Date: Thu, 22 Oct 2015 19:12:34 +0200 Message-ID: <1445533954-19857-1-git-send-email-vkuznets@redhat.com> Return-path: Sender: linux-kernel-owner@vger.kernel.org To: "James E.J. Bottomley" Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, "K. Y. Srinivasan" List-Id: linux-scsi@vger.kernel.org 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:[] [] bdi_destroy+0x39/0x220 ... [] ? _raw_spin_unlock_irq+0x2c/0x40 [] blk_cleanup_queue+0x17b/0x270 [] __scsi_remove_device+0x54/0xd0 [scsi_mod] [] scsi_remove_device+0x2b/0x40 [scsi_mod] [] storvsc_remove_lun+0x3d/0x60 [hv_storvsc] [] 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 all of them, after that both callers 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 --- drivers/scsi/scsi_sysfs.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c index b333389..e0d2707 100644 --- a/drivers/scsi/scsi_sysfs.c +++ b/drivers/scsi/scsi_sysfs.c @@ -1076,6 +1076,14 @@ void __scsi_remove_device(struct scsi_device *sdev) { struct device *dev = &sdev->sdev_gendev; + /* + * This cleanup path is not reentrant and while it is impossible + * to get a new reference with scsi_device_get() someone can still + * hold a previously acquired one. + */ + if (sdev->sdev_state == SDEV_DEL) + return; + if (sdev->is_visible) { if (scsi_device_set_state(sdev, SDEV_CANCEL) != 0) return; -- 2.4.3