Re: [PATCH] scsi_sysfs: protect against double execution of __scsi_remove_device()
Bart Van Asschewrites: > On 10/22/2015 10:12 AM, Vitaly Kuznetsov wrote: >> 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: [#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 b89..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_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; > > Hello Vitaly, > > Sorry but I don't see how the above patch could be a proper fix. If > two calls to __scsi_remove_device() occur concurrently the crash > explained above can still occur. The storsvc driver should be modified > such that concurrent __scsi_remove_device() calls do not occur. How > about preventing concurrent calls via a mutex ? Nobody is supposed to call __scsi_remove_device() without holding shost->scan_mutex and scsi_remove_device() does that. Here I'm trying to protect against two *consequent* calls to the __scsi_remove_device(). As we set sdev_state to SDEV_DEL on the cleanup path checking it should be enough. > Another possible > approach is to use the workqueue mechanism. An example can be found in > the SRP initiator driver (ib_srp). Yes, but I think the existent approach is good enough: 1) Every caller is supposed to get a reference to the device with scsi_device_get() (scsi_device_lookup() does that). 2) shost->scan_mutex is suppose to be held by all __scsi_remove_device() callers. -- Vitaly -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] scsi_sysfs: protect against double execution of __scsi_remove_device()
On 10/22/2015 10:12 AM, Vitaly Kuznetsov wrote: 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: [#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 b89..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_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; Hello Vitaly, Sorry but I don't see how the above patch could be a proper fix. If two calls to __scsi_remove_device() occur concurrently the crash explained above can still occur. The storsvc driver should be modified such that concurrent __scsi_remove_device() calls do not occur. How about preventing concurrent calls via a mutex ? Another possible approach is to use the workqueue mechanism. An example can be found in the SRP initiator driver (ib_srp). Bart. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH] 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: [#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 b89..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_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 -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html