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

From: Vitaly Kuznetsov
Date: Fri Nov 06 2015 - 10:49:37 EST

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) {

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>
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 dff8faf..3b7e2bb 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -1078,6 +1078,14 @@ 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)

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