Re: [PATCH] pstore: change mutex locking to spin_locks

From: Huang Ying
Date: Wed Jul 20 2011 - 20:40:44 EST


On 07/21/2011 04:56 AM, Don Zickus wrote:
> pstore was using mutex locking to protect read/write access to the
> backend plug-ins. This causes problems when pstore is executed in
> an NMI context through panic() -> kmsg_dump().
>
> This patch changes the mutex to a spin_lock_irqsave then also checks to
> see if we are in an NMI context. If we are in an NMI and can't get the
> lock, just print a message stating that and blow by the locking.
>
> All this is probably a hack around the bigger locking problem but it
> solves my current situation of trying to sleep in an NMI context.
>
> Tested by loading the lkdtm module and executing a HARDLOCKUP which
> will cause the machine to panic inside the nmi handler.
>
> Signed-off-by: Don Zickus <dzickus@xxxxxxxxxx>
> ---
> drivers/acpi/apei/erst.c | 2 +-
> fs/pstore/platform.c | 28 ++++++++++++++++++++++------
> include/linux/pstore.h | 2 +-
> 3 files changed, 24 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/acpi/apei/erst.c b/drivers/acpi/apei/erst.c
> index e6cef8e..3d9c2a3 100644
> --- a/drivers/acpi/apei/erst.c
> +++ b/drivers/acpi/apei/erst.c
> @@ -1155,7 +1155,7 @@ static int __init erst_init(void)
> goto err_release_erange;
>
> buf = kmalloc(erst_erange.size, GFP_KERNEL);
> - mutex_init(&erst_info.buf_mutex);
> + spin_lock_init(&erst_info.buf_lock);
> if (buf) {
> erst_info.buf = buf + sizeof(struct cper_pstore_record);
> erst_info.bufsize = erst_erange.size -
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index f2c3ff2..53ba00b 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -27,6 +27,7 @@
> #include <linux/string.h>
> #include <linux/slab.h>
> #include <linux/uaccess.h>
> +#include <linux/hardirq.h>
>
> #include "internal.h"
>
> @@ -68,13 +69,21 @@ static void pstore_dump(struct kmsg_dumper *dumper,
> char *dst, *why;
> u64 id;
> int hsize, part = 1;
> + unsigned long flags = 0;
> + int is_locked = 0;
>
> if (reason < ARRAY_SIZE(reason_str))
> why = reason_str[reason];
> else
> why = "Unknown";
>
> - mutex_lock(&psinfo->buf_mutex);
> + if (in_nmi()) {
> + is_locked = spin_trylock(&psinfo->buf_lock);
> + if (!is_locked)
> + pr_err("pstore dump routine blocked in NMI, may corrupt error record\n");
> + } else {
> + spin_lock_irqsave(&psinfo->buf_lock, flags);
> + }
> oopscount++;
> while (total < kmsg_bytes) {
> dst = psinfo->buf;
> @@ -103,7 +112,12 @@ static void pstore_dump(struct kmsg_dumper *dumper,
> l2 -= l2_cpy;
> total += l1_cpy + l2_cpy;
> }
> - mutex_unlock(&psinfo->buf_mutex);
> + if (in_nmi()) {
> + if (is_locked)
> + spin_unlock(&psinfo->buf_lock);
> + } else {
> + spin_unlock_irqrestore(&psinfo->buf_lock, flags);
> + }
> }
>
> static struct kmsg_dumper pstore_dumper = {
> @@ -157,11 +171,12 @@ void pstore_get_records(void)
> enum pstore_type_id type;
> struct timespec time;
> int failed = 0, rc;
> + unsigned long flags;
>
> if (!psi)
> return;
>
> - mutex_lock(&psinfo->buf_mutex);
> + spin_lock_irqsave(&psinfo->buf_lock, flags);
> rc = psi->open(psi);
> if (rc)
> goto out;
> @@ -173,7 +188,7 @@ void pstore_get_records(void)
> }
> psi->close(psi);
> out:
> - mutex_unlock(&psinfo->buf_mutex);
> + spin_unlock_irqrestore(&psinfo->buf_lock, flags);
>
> if (failed)
> printk(KERN_WARNING "pstore: failed to load %d record(s) from '%s'\n",
> @@ -187,6 +202,7 @@ out:
> int pstore_write(enum pstore_type_id type, char *buf, size_t size)
> {
> u64 id;
> + unsigned long flags;
>
> if (!psinfo)
> return -ENODEV;
> @@ -194,13 +210,13 @@ int pstore_write(enum pstore_type_id type, char *buf, size_t size)
> if (size > psinfo->bufsize)
> return -EFBIG;
>
> - mutex_lock(&psinfo->buf_mutex);
> + spin_lock_irqsave(&psinfo->buf_lock, flags);
> memcpy(psinfo->buf, buf, size);
> id = psinfo->write(type, size);
> if (pstore_is_mounted())
> pstore_mkfile(PSTORE_TYPE_DMESG, psinfo->name, id, psinfo->buf,
> size, CURRENT_TIME, psinfo->erase);
> - mutex_unlock(&psinfo->buf_mutex);
> + spin_unlock_irqrestore(&psinfo->buf_lock, flags);

Is it safe to call pstore_mkfile with IRQ disabled?

pstore_mkfile -> d_alloc_name -> d_alloc -> kmem_cache_alloc(, GFP_KERNEL).

Best Regards,
Huang Ying
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