On 29.03.23 09:20, Juergen Gross wrote: Hello Juergen > On 28.03.23 17:47, Oleksandr Tyshchenko wrote: >> >> >> On 28.03.23 11:46, Juergen Gross wrote: >> >> Hello Juergen >> >>> scsiback_free_translation_entry() shouldn't be called under spinlock, >>> as it can sleep. >>> >>> This requires to split removing a translation entry from the v2p list >>> from actually calling kref_put() for the entry. >>> >>> Reported-by: Dan Carpenter <error27@xxxxxxxxx> >>> Link: >>> https://urldefense.com/v3/__https://lore.kernel.org/lkml/Y*JUIl64UDmdkboh@kadam/__;Kw!!GF_29dbcQIUBPA!23IKdVhamoFq8ptUnprd_TubDMObj-0QAalsGiffBHCeEdOuwrq7z4ohg92Sj0olgl0nh73oXvSr-i1zqXhY$ [lore[.]kernel[.]org] >>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx> >>> --- >>> drivers/xen/xen-scsiback.c | 27 ++++++++++++++------------- >>> 1 file changed, 14 insertions(+), 13 deletions(-) >>> >>> diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c >>> index 954188b0b858..294f29cdc7aa 100644 >>> --- a/drivers/xen/xen-scsiback.c >>> +++ b/drivers/xen/xen-scsiback.c >>> @@ -1010,12 +1010,6 @@ static int >>> scsiback_add_translation_entry(struct vscsibk_info *info, >>> return err; >>> } >>> -static void __scsiback_del_translation_entry(struct v2p_entry *entry) >>> -{ >>> - list_del(&entry->l); >>> - kref_put(&entry->kref, scsiback_free_translation_entry); >>> -} >>> - >>> /* >>> Delete the translation entry specified >>> */ >>> @@ -1024,18 +1018,20 @@ static int >>> scsiback_del_translation_entry(struct vscsibk_info *info, >>> { >>> struct v2p_entry *entry; >>> unsigned long flags; >>> - int ret = 0; >>> spin_lock_irqsave(&info->v2p_lock, flags); >>> /* Find out the translation entry specified */ >>> entry = scsiback_chk_translation_entry(info, v); >>> if (entry) >>> - __scsiback_del_translation_entry(entry); >>> - else >>> - ret = -ENOENT; >>> + list_del(&entry->l); >>> spin_unlock_irqrestore(&info->v2p_lock, flags); >>> - return ret; >>> + >>> + if (!entry) >>> + return -ENOENT; >>> + >>> + kref_put(&entry->kref, scsiback_free_translation_entry); >>> + return 0; >>> } >>> static void scsiback_do_add_lun(struct vscsibk_info *info, const >>> char *state, >>> @@ -1239,14 +1235,19 @@ static void >>> scsiback_release_translation_entry(struct vscsibk_info *info) >>> { >>> struct v2p_entry *entry, *tmp; >>> struct list_head *head = &(info->v2p_entry_lists); >>> + struct list_head tmp_list; >> >> >> I would use LIST_HEAD(tmp_list); > > There is no need to initialize it, so I think I will keep it as is. > >> >>> unsigned long flags; >>> spin_lock_irqsave(&info->v2p_lock, flags); >>> - list_for_each_entry_safe(entry, tmp, head, l) >>> - __scsiback_del_translation_entry(entry); >>> + list_cut_before(&tmp_list, head, head); >> >> so we just move all entries from head to tmp_list here to be processed... > > Correct. > >> >>> spin_unlock_irqrestore(&info->v2p_lock, flags); >> >> ... when the lock is not held, ok >> >> Patch LGTM, but one (maybe stupid) question to clarify. >> >> Why do we need to use a lock here in the first place? The >> scsiback_release_translation_entry() gets called when the driver >> instance is about to be removed and *after* the disconnection from >> otherend (so no requests are expected), so what else might cause this >> list to be accessed concurrently? > > Maybe nothing, but I think it is good practice to keep the lock in order > to avoid future code changes to cause problems. Thanks for the explanation, it sounds reasonable to me. Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx> > > > Juergen >
