RE: [PATCH v3] efivars,efi-pstore: Hold off deletion of sysfs entryuntil, the scan is completed

From: Seiji Aguchi
Date: Thu Oct 17 2013 - 09:08:05 EST

Hi Madper,

I tested this patch on 3.12-rc4.
Could you please send me the log when you failed to apply?

Seiji

> -----Original Message-----
> From: Madper Xie [mailto:cxie@xxxxxxxxxx]
> Sent: Thursday, October 17, 2013 1:54 AM
> To: Seiji Aguchi
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-efi@xxxxxxxxxxxxxxx; matt.fleming@xxxxxxxxx; tony.luck@xxxxxxxxx; Tomoki Sekiyama; dle-
> develop@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v3] efivars,efi-pstore: Hold off deletion of sysfs entry until, the scan is completed
>
> Howdy Seiji,
> I failed appily this patch to both 3.12-rc2 and 3.12-rc4. Could you
> please let me know which is the right tree for this patch?
>
> Thanks,
> Madper.
> seiji.aguchi@xxxxxxx writes:
>
> > Change from v2:
> > - Move dynamic memory allocation to efi_pstore_read() before holding
> > efivars->lock to protect entry->var.Data.
> > - Access to entry->scanning while holding efivars->lock.
> > - Move a comment about a returned value from efi_pstore_read_func() to
> > efi_pstore_read() because "size < 0" case may happen in efi_pstore_read().
> >
> > Currently, when mounting pstore file system, a read callback of efi_pstore
> > driver runs mutiple times as below.
> >
> > - In the first read callback, scan efivar_sysfs_list from head and pass
> > a kmsg buffer of a entry to an upper pstore layer.
> > - In the second read callback, rescan efivar_sysfs_list from the entry and pass
> > another kmsg buffer to it.
> > - Repeat the scan and pass until the end of efivar_sysfs_list.
> >
> > In this process, an entry is read across the multiple read function calls.
> > To avoid race between the read and erasion, the whole process above is
> > protected by a spinlock, holding in open() and releasing in close().
> >
> > At the same time, kmemdup() is called to pass the buffer to pstore filesystem
> > during it.
> > And then, it causes a following lockdep warning.
> >
> > To make the dynamic memory allocation runnable without taking spinlock,
> > holding off a deletion of sysfs entry if it happens while scanning it
> > via efi_pstore, and deleting it after the scan is completed.
> >
> > To implement it, this patch introduces two flags, scanning and deleting,
> > to efivar_entry.
> >
> > [ 1.143710] ------------[ cut here ]------------
> > [ 1.144058] WARNING: CPU: 1 PID: 1 at kernel/lockdep.c:2740
> > lockdep_trace_alloc+0x104/0x110()
> > [ 1.144058] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
> > [ 1.144058] Modules linked in:
> >
> > [ 1.144058] CPU: 1 PID: 1 Comm: systemd Not tainted 3.11.0-rc5 #2
> > [ 1.144058] 0000000000000009 ffff8800797e9ae0 ffffffff816614a5
> > ffff8800797e9b28
> > [ 1.144058] ffff8800797e9b18 ffffffff8105510d 0000000000000080
> > 0000000000000046
> > [ 1.144058] 00000000000000d0 00000000000003af ffffffff81ccd0c0
> > ffff8800797e9b78
> > [ 1.144058] Call Trace:
> > [ 1.144058] [<ffffffff816614a5>] dump_stack+0x54/0x74
> > [ 1.144058] [<ffffffff8105510d>] warn_slowpath_common+0x7d/0xa0
> > [ 1.144058] [<ffffffff8105517c>] warn_slowpath_fmt+0x4c/0x50
> > [ 1.144058] [<ffffffff8131290f>] ? vsscanf+0x57f/0x7b0
> > [ 1.144058] [<ffffffff810bbd74>] lockdep_trace_alloc+0x104/0x110
> > [ 1.144058] [<ffffffff81192da0>] __kmalloc_track_caller+0x50/0x280
> > [ 1.144058] [<ffffffff815147bb>] ?
> > efi_pstore_read_func.part.1+0x12b/0x170
> > [ 1.144058] [<ffffffff8115b260>] kmemdup+0x20/0x50
> > [ 1.144058] [<ffffffff815147bb>] efi_pstore_read_func.part.1+0x12b/0x170
> > [ 1.144058] [<ffffffff81514800>] ?
> > efi_pstore_read_func.part.1+0x170/0x170
> > [ 1.144058] [<ffffffff815148b4>] efi_pstore_read_func+0xb4/0xe0
> > [ 1.144058] [<ffffffff81512b7b>] __efivar_entry_iter+0xfb/0x120
> > [ 1.144058] [<ffffffff8151428f>] efi_pstore_read+0x3f/0x50
> > [ 1.144058] [<ffffffff8128d7ba>] pstore_get_records+0x9a/0x150
> > [ 1.158207] [<ffffffff812af25c>] ? selinux_d_instantiate+0x1c/0x20
> > [ 1.158207] [<ffffffff8128ce30>] ? parse_options+0x80/0x80
> > [ 1.158207] [<ffffffff8128ced5>] pstore_fill_super+0xa5/0xc0
> > [ 1.158207] [<ffffffff811ae7d2>] mount_single+0xa2/0xd0
> > [ 1.158207] [<ffffffff8128ccf8>] pstore_mount+0x18/0x20
> > [ 1.158207] [<ffffffff811ae8b9>] mount_fs+0x39/0x1b0
> > [ 1.158207] [<ffffffff81160550>] ? __alloc_percpu+0x10/0x20
> > [ 1.158207] [<ffffffff811c9493>] vfs_kern_mount+0x63/0xf0
> > [ 1.158207] [<ffffffff811cbb0e>] do_mount+0x23e/0xa20
> > [ 1.158207] [<ffffffff8115b51b>] ? strndup_user+0x4b/0xf0
> > [ 1.158207] [<ffffffff811cc373>] SyS_mount+0x83/0xc0
> > [ 1.158207] [<ffffffff81673cc2>] system_call_fastpath+0x16/0x1b
> > [ 1.158207] ---[ end trace 61981bc62de9f6f4 ]---
> >
> > Signed-off-by: Seiji Aguchi <seiji.aguchi@xxxxxxx>
> > ---
> > drivers/firmware/efi/efi-pstore.c | 143 +++++++++++++++++++++++++++++++++++---
> > drivers/firmware/efi/efivars.c | 12 ++--
> > drivers/firmware/efi/vars.c | 12 +++-
> > include/linux/efi.h | 2 +
> > 4 files changed, 153 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c
> > index 5002d50..ebd5dbc 100644
> > --- a/drivers/firmware/efi/efi-pstore.c
> > +++ b/drivers/firmware/efi/efi-pstore.c
> > @@ -18,14 +18,12 @@ module_param_named(pstore_disable, efivars_pstore_disable, bool, 0644);
> >
> > static int efi_pstore_open(struct pstore_info *psi)
> > {
> > - efivar_entry_iter_begin();
> > psi->data = NULL;
> > return 0;
> > }
> >
> > static int efi_pstore_close(struct pstore_info *psi)
> > {
> > - efivar_entry_iter_end();
> > psi->data = NULL;
> > return 0;
> > }
> > @@ -91,19 +89,125 @@ static int efi_pstore_read_func(struct efivar_entry *entry, void *data)
> > __efivar_entry_get(entry, &entry->var.Attributes,
> > &entry->var.DataSize, entry->var.Data);
> > size = entry->var.DataSize;
> > + memcpy(*cb_data->buf, entry->var.Data, (size_t)min_t(unsigned long,
> > + 1024, size));
> >
> > - *cb_data->buf = kmemdup(entry->var.Data, size, GFP_KERNEL);
> > - if (*cb_data->buf == NULL)
> > - return -ENOMEM;
> > return size;
> > }
> >
> > +/**
> > + * efi_pstore_scan_sysfs_enter
> > + * @entry: scanning entry
> > + * @next: next entry
> > + * @head: list head
> > + */
> > +static void efi_pstore_scan_sysfs_enter(struct efivar_entry *pos,
> > + struct efivar_entry *next,
> > + struct list_head *head)
> > +{
> > + pos->scanning = true;
> > + if (&next->list != head)
> > + next->scanning = true;
> > +}
> > +
> > +/**
> > + * __efi_pstore_scan_sysfs_exit
> > + * @entry: deleting entry
> > + * @turn_off_scanning: Check if a scanning flag should be turned off
> > + */
> > +static inline void __efi_pstore_scan_sysfs_exit(struct efivar_entry *entry,
> > + bool turn_off_scanning)
> > +{
> > + if (entry->deleting) {
> > + list_del(&entry->list);
> > + efivar_entry_iter_end();
> > + efivar_unregister(entry);
> > + efivar_entry_iter_begin();
> > + } else if (turn_off_scanning)
> > + entry->scanning = false;
> > +}
> > +
> > +/**
> > + * efi_pstore_scan_sysfs_exit
> > + * @pos: scanning entry
> > + * @next: next entry
> > + * @head: list head
> > + * @stop: a flag checking if scanning will stop
> > + */
> > +static void efi_pstore_scan_sysfs_exit(struct efivar_entry *pos,
> > + struct efivar_entry *next,
> > + struct list_head *head, bool stop)
> > +{
> > + __efi_pstore_scan_sysfs_exit(pos, true);
> > + if (stop)
> > + __efi_pstore_scan_sysfs_exit(next, &next->list != head);
> > +}
> > +
> > +/**
> > + * efi_pstore_sysfs_entry_iter
> > + *
> > + * @data: function-specific data to pass to callback
> > + * @pos: entry to begin iterating from
> > + *
> > + * You MUST call efivar_enter_iter_begin() before this function, and
> > + * efivar_entry_iter_end() afterwards.
> > + *
> > + * It is possible to begin iteration from an arbitrary entry within
> > + * the list by passing @pos. @pos is updated on return to point to
> > + * the next entry of the last one passed to efi_pstore_read_func().
> > + * To begin iterating from the beginning of the list @pos must be %NULL.
> > + */
> > +static int efi_pstore_sysfs_entry_iter(void *data, struct efivar_entry **pos)
> > +{
> > + struct efivar_entry *entry, *n;
> > + struct list_head *head = &efivar_sysfs_list;
> > + int size = 0;
> > +
> > + if (!*pos) {
> > + list_for_each_entry_safe(entry, n, head, list) {
> > + efi_pstore_scan_sysfs_enter(entry, n, head);
> > +
> > + size = efi_pstore_read_func(entry, data);
> > + efi_pstore_scan_sysfs_exit(entry, n, head, size < 0);
> > + if (size)
> > + break;
> > + }
> > + *pos = n;
> > + return size;
> > + }
> > +
> > + list_for_each_entry_safe_from((*pos), n, head, list) {
> > + efi_pstore_scan_sysfs_enter((*pos), n, head);
> > +
> > + size = efi_pstore_read_func((*pos), data);
> > + efi_pstore_scan_sysfs_exit((*pos), n, head, size < 0);
> > + if (size)
> > + break;
> > + }
> > + *pos = n;
> > + return size;
> > +}
> > +
> > +/**
> > + * efi_pstore_read
> > + *
> > + * This function returns a size of NVRAM entry logged via efi_pstore_write().
> > + * The meaning and behavior of efi_pstore/pstore are as below.
> > + *
> > + * size > 0: Got data of an entry logged via efi_pstore_write() successfully,
> > + * and pstore filesystem will continue reading subsequent entries.
> > + * size == 0: Entry was not logged via efi_pstore_write(),
> > + * and efi_pstore driver will continue reading subsequent entries.
> > + * size < 0: Failed to get data of entry logging via efi_pstore_write(),
> > + * and pstore will stop reading entry.
> > + */
> > static ssize_t efi_pstore_read(u64 *id, enum pstore_type_id *type,
> > int *count, struct timespec *timespec,
> > char **buf, bool *compressed,
> > struct pstore_info *psi)
> > {
> > struct pstore_read_data data;
> > + ssize_t size;
> >
> > data.id = id;
> > data.type = type;
> > @@ -112,8 +216,17 @@ static ssize_t efi_pstore_read(u64 *id, enum pstore_type_id *type,
> > data.compressed = compressed;
> > data.buf = buf;
> >
> > - return __efivar_entry_iter(efi_pstore_read_func, &efivar_sysfs_list, &data,
> > - (struct efivar_entry **)&psi->data);
> > + *data.buf = kzalloc(1024, GFP_KERNEL);
> > + if (!*data.buf)
> > + return -ENOMEM;
> > +
> > + efivar_entry_iter_begin();
> > + size = efi_pstore_sysfs_entry_iter(&data,
> > + (struct efivar_entry **)&psi->data);
> > + efivar_entry_iter_end();
> > + if (size <= 0)
> > + kfree(*data.buf);
> > + return size;
> > }
> >
> > static int efi_pstore_write(enum pstore_type_id type,
> > @@ -184,9 +297,17 @@ static int efi_pstore_erase_func(struct efivar_entry *entry, void *data)
> > return 0;
> > }
> >
> > + if (entry->scanning) {
> > + /*
> > + * Skip deletion because this entry will be deleted
> > + * after scanning is completed.
> > + */
> > + entry->deleting = true;
> > + } else
> > + list_del(&entry->list);
> > +
> > /* found */
> > __efivar_entry_delete(entry);
> > - list_del(&entry->list);
> >
> > return 1;
> > }
> > @@ -214,10 +335,12 @@ static int efi_pstore_erase(enum pstore_type_id type, u64 id, int count,
> >
> > efivar_entry_iter_begin();
> > found = __efivar_entry_iter(efi_pstore_erase_func, &efivar_sysfs_list, &edata, &entry);
> > - efivar_entry_iter_end();
> >
> > - if (found)
> > + if (found && !entry->scanning) {
> > + efivar_entry_iter_end();
> > efivar_unregister(entry);
> > + } else
> > + efivar_entry_iter_end();
> >
> > return 0;
> > }
> > diff --git a/drivers/firmware/efi/efivars.c b/drivers/firmware/efi/efivars.c
> > index 8a7432a..8c5a61a 100644
> > --- a/drivers/firmware/efi/efivars.c
> > +++ b/drivers/firmware/efi/efivars.c
> > @@ -383,12 +383,16 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj,
> > else if (__efivar_entry_delete(entry))
> > err = -EIO;
> >
> > - efivar_entry_iter_end();
> > -
> > - if (err)
> > + if (err) {
> > + efivar_entry_iter_end();
> > return err;
> > + }
> >
> > - efivar_unregister(entry);
> > + if (!entry->scanning) {
> > + efivar_entry_iter_end();
> > + efivar_unregister(entry);
> > + } else
> > + efivar_entry_iter_end();
> >
> > /* It's dead Jim.... */
> > return count;
> > diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
> > index 391c67b..b22659c 100644
> > --- a/drivers/firmware/efi/vars.c
> > +++ b/drivers/firmware/efi/vars.c
> > @@ -683,8 +683,16 @@ struct efivar_entry *efivar_entry_find(efi_char16_t *name, efi_guid_t guid,
> > if (!found)
> > return NULL;
> >
> > - if (remove)
> > - list_del(&entry->list);
> > + if (remove) {
> > + if (entry->scanning) {
> > + /*
> > + * The entry will be deleted
> > + * after scanning is completed.
> > + */
> > + entry->deleting = true;
> > + } else
> > + list_del(&entry->list);
> > + }
> >
> > return entry;
> > }
> > diff --git a/include/linux/efi.h b/include/linux/efi.h
> > index 5f8f176..04088fb 100644
> > --- a/include/linux/efi.h
> > +++ b/include/linux/efi.h
> > @@ -782,6 +782,8 @@ struct efivar_entry {
> > struct efi_variable var;
> > struct list_head list;
> > struct kobject kobj;
> > + bool scanning;
> > + bool deleting;
> > };
> >
> > extern struct list_head efivar_sysfs_list;
>
>
> --
> Best,
> Madper Xie.
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