From 9f244e9cfd70c7c0f82d3c92ce772ab2a92d9f64 Mon Sep 17 00:00:00 2001 From: Seiji Aguchi Date: Fri, 11 Jan 2013 18:09:41 +0000 Subject: pstore: Avoid deadlock in panic and emergency-restart path [Issue] When pstore is in panic and emergency-restart paths, it may be blocked in those paths because it simply takes spin_lock. This is an example scenario which pstore may hang up in a panic path: - cpuA grabs psinfo->buf_lock - cpuB panics and calls smp_send_stop - smp_send_stop sends IRQ to cpuA - after 1 second, cpuB gives up on cpuA and sends an NMI instead - cpuA is now in an NMI handler while still holding buf_lock - cpuB is deadlocked This case may happen if a firmware has a bug and cpuA is stuck talking with it more than one second. Also, this is a similar scenario in an emergency-restart path: - cpuA grabs psinfo->buf_lock and stucks in a firmware - cpuB kicks emergency-restart via either sysrq-b or hangcheck timer. And then, cpuB is deadlocked by taking psinfo->buf_lock again. [Solution] This patch avoids the deadlocking issues in both panic and emergency_restart paths by introducing a function, is_non_blocking_path(), to check if a cpu can be blocked in current path. With this patch, pstore is not blocked even if another cpu has taken a spin_lock, in those paths by changing from spin_lock_irqsave to spin_trylock_irqsave. In addition, according to a comment of emergency_restart() in kernel/sys.c, spin_lock shouldn't be taken in an emergency_restart path to avoid deadlock. This patch fits the comment below. /** * emergency_restart - reboot the system * * Without shutting down any hardware or taking any locks * reboot the system. This is called when we know we are in * trouble so this is our best effort to reboot. This is * safe to call in interrupt context. */ void emergency_restart(void) Signed-off-by: Seiji Aguchi Acked-by: Don Zickus Signed-off-by: Tony Luck --- fs/pstore/platform.c | 35 +++++++++++++++++++++++++++++------ 1 file changed, 29 insertions(+), 6 deletions(-) (limited to 'fs/pstore') diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c index 5ea2e77ff023..86d1038b5a12 100644 --- a/fs/pstore/platform.c +++ b/fs/pstore/platform.c @@ -96,6 +96,27 @@ static const char *get_reason_str(enum kmsg_dump_reason reason) } } +bool pstore_cannot_block_path(enum kmsg_dump_reason reason) +{ + /* + * In case of NMI path, pstore shouldn't be blocked + * regardless of reason. + */ + if (in_nmi()) + return true; + + switch (reason) { + /* In panic case, other cpus are stopped by smp_send_stop(). */ + case KMSG_DUMP_PANIC: + /* Emergency restart shouldn't be blocked by spin lock. */ + case KMSG_DUMP_EMERG: + return true; + default: + return false; + } +} +EXPORT_SYMBOL_GPL(pstore_cannot_block_path); + /* * callback from kmsg_dump. (s2,l2) has the most recently * written bytes, older bytes are in (s1,l1). Save as much @@ -114,10 +135,12 @@ static void pstore_dump(struct kmsg_dumper *dumper, why = get_reason_str(reason); - 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"); + if (pstore_cannot_block_path(reason)) { + is_locked = spin_trylock_irqsave(&psinfo->buf_lock, flags); + if (!is_locked) { + pr_err("pstore dump routine blocked in %s path, may corrupt error record\n" + , in_nmi() ? "NMI" : why); + } } else spin_lock_irqsave(&psinfo->buf_lock, flags); oopscount++; @@ -143,9 +166,9 @@ static void pstore_dump(struct kmsg_dumper *dumper, total += hsize + len; part++; } - if (in_nmi()) { + if (pstore_cannot_block_path(reason)) { if (is_locked) - spin_unlock(&psinfo->buf_lock); + spin_unlock_irqrestore(&psinfo->buf_lock, flags); } else spin_unlock_irqrestore(&psinfo->buf_lock, flags); } -- cgit v1.2.3 From fb0af3f2b1b613e5ea75426d454c7e5b1d1eef49 Mon Sep 17 00:00:00 2001 From: Josh Boyer Date: Tue, 12 Feb 2013 13:07:22 -0800 Subject: pstore: Create a convenient mount point for pstore Using /dev/pstore as a mount point for the pstore filesystem is slightly awkward. We don't normally mount filesystems in /dev/ and the /dev/pstore file isn't created automatically by anything. While this method will still work, we can create a persistent mount point in sysfs. This will put pstore on par with things like cgroups and efivarfs. Signed-off-by: Josh Boyer Acked-by: Kees Cook Signed-off-by: Tony Luck --- Documentation/ABI/testing/pstore | 10 +++++----- fs/pstore/inode.c | 18 +++++++++++++++++- 2 files changed, 22 insertions(+), 6 deletions(-) (limited to 'fs/pstore') diff --git a/Documentation/ABI/testing/pstore b/Documentation/ABI/testing/pstore index ff1df4e3b059..5fca9f5e10a3 100644 --- a/Documentation/ABI/testing/pstore +++ b/Documentation/ABI/testing/pstore @@ -1,4 +1,4 @@ -Where: /dev/pstore/... +Where: /sys/fs/pstore/... (or /dev/pstore/...) Date: March 2011 Kernel Version: 2.6.39 Contact: tony.luck@intel.com @@ -11,9 +11,9 @@ Description: Generic interface to platform dependent persistent storage. of the console log is captured, but other interesting data can also be saved. - # mount -t pstore -o kmsg_bytes=8000 - /dev/pstore + # mount -t pstore -o kmsg_bytes=8000 - /sys/fs/pstore - $ ls -l /dev/pstore + $ ls -l /sys/fs/pstore/ total 0 -r--r--r-- 1 root root 7896 Nov 30 15:38 dmesg-erst-1 @@ -27,9 +27,9 @@ Description: Generic interface to platform dependent persistent storage. the file will signal to the underlying persistent storage device that it can reclaim the space for later re-use. - $ rm /dev/pstore/dmesg-erst-1 + $ rm /sys/fs/pstore/dmesg-erst-1 - The expectation is that all files in /dev/pstore + The expectation is that all files in /sys/fs/pstore/ will be saved elsewhere and erased from persistent store soon after boot to free up space ready for the next catastrophe. diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c index 67de74ca85f4..e4bcb2cf055a 100644 --- a/fs/pstore/inode.c +++ b/fs/pstore/inode.c @@ -418,9 +418,25 @@ static struct file_system_type pstore_fs_type = { .kill_sb = pstore_kill_sb, }; +static struct kobject *pstore_kobj; + static int __init init_pstore_fs(void) { - return register_filesystem(&pstore_fs_type); + int err = 0; + + /* Create a convenient mount point for people to access pstore */ + pstore_kobj = kobject_create_and_add("pstore", fs_kobj); + if (!pstore_kobj) { + err = -ENOMEM; + goto out; + } + + err = register_filesystem(&pstore_fs_type); + if (err < 0) + kobject_put(pstore_kobj); + +out: + return err; } module_init(init_pstore_fs) -- cgit v1.2.3