Hi Michael,
Thanks for the patch, the patch looks fine to me.
Tested-by: Kajol Jain<kj...@linux.ibm.com>
Reviewed-by: Kajol Jain<kj...@linux.ibm.com>
Thanks,
Kajol Jain
On 8/19/24 17:54, Michael Ellerman wrote:
> The dtl_access_lock needs to be a rw_sempahore, a sleeping lock, because
> the code calls kmalloc() while holding it, which can sleep:
>
> # echo 1 > /proc/powerpc/vcpudispatch_stats
> BUG: sleeping function called from invalid context at
> include/linux/sched/mm.h:337
> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 199, name: sh
> preempt_count: 1, expected: 0
> 3 locks held by sh/199:
> #0: c00000000a0743f8 (sb_writers#3){.+.+}-{0:0}, at: vfs_write+0x324/0x438
> #1: c0000000028c7058 (dtl_enable_mutex){+.+.}-{3:3}, at:
> vcpudispatch_stats_write+0xd4/0x5f4
> #2: c0000000028c70b8 (dtl_access_lock){+.+.}-{2:2}, at:
> vcpudispatch_stats_write+0x220/0x5f4
> CPU: 0 PID: 199 Comm: sh Not tainted 6.10.0-rc4 #152
> Hardware name: IBM pSeries (emulated by qemu) POWER9 (raw) 0x4e1202
> 0xf000005 of:SLOF,HEAD hv:linux,kvm pSeries
> Call Trace:
> dump_stack_lvl+0x130/0x148 (unreliable)
> __might_resched+0x174/0x410
> kmem_cache_alloc_noprof+0x340/0x3d0
> alloc_dtl_buffers+0x124/0x1ac
> vcpudispatch_stats_write+0x2a8/0x5f4
> proc_reg_write+0xf4/0x150
> vfs_write+0xfc/0x438
> ksys_write+0x88/0x148
> system_call_exception+0x1c4/0x5a0
> system_call_common+0xf4/0x258
>
> Fixes: 06220d78f24a ("powerpc/pseries: Introduce rwlock to gatekeep DTLB
> usage")
> Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
> ---
> arch/powerpc/include/asm/dtl.h | 3 ++-
> arch/powerpc/platforms/pseries/dtl.c | 8 ++++----
> arch/powerpc/platforms/pseries/lpar.c | 8 ++++----
> 3 files changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/dtl.h b/arch/powerpc/include/asm/dtl.h
> index d6f43d149f8d..e21bac6c065c 100644
> --- a/arch/powerpc/include/asm/dtl.h
> +++ b/arch/powerpc/include/asm/dtl.h
> @@ -1,6 +1,7 @@
> #ifndef _ASM_POWERPC_DTL_H
> #define _ASM_POWERPC_DTL_H
>
> +#include <linux/rwsem.h>
> #include <asm/lppaca.h>
> #include <linux/spinlock_types.h>
>
> @@ -35,7 +36,7 @@ struct dtl_entry {
> #define DTL_LOG_ALL (DTL_LOG_CEDE | DTL_LOG_PREEMPT | DTL_LOG_FAULT)
>
> extern struct kmem_cache *dtl_cache;
> -extern rwlock_t dtl_access_lock;
> +extern struct rw_semaphore dtl_access_lock;
>
> extern void register_dtl_buffer(int cpu);
> extern void alloc_dtl_buffers(unsigned long *time_limit);
> diff --git a/arch/powerpc/platforms/pseries/dtl.c
> b/arch/powerpc/platforms/pseries/dtl.c
> index 3f1cdccebc9c..ecc04ef8c53e 100644
> --- a/arch/powerpc/platforms/pseries/dtl.c
> +++ b/arch/powerpc/platforms/pseries/dtl.c
> @@ -191,7 +191,7 @@ static int dtl_enable(struct dtl *dtl)
> return -EBUSY;
>
> /* ensure there are no other conflicting dtl users */
> - if (!read_trylock(&dtl_access_lock))
> + if (!down_read_trylock(&dtl_access_lock))
> return -EBUSY;
>
> n_entries = dtl_buf_entries;
> @@ -199,7 +199,7 @@ static int dtl_enable(struct dtl *dtl)
> if (!buf) {
> printk(KERN_WARNING "%s: buffer alloc failed for cpu %d\n",
> __func__, dtl->cpu);
> - read_unlock(&dtl_access_lock);
> + up_read(&dtl_access_lock);
> return -ENOMEM;
> }
>
> @@ -217,7 +217,7 @@ static int dtl_enable(struct dtl *dtl)
> spin_unlock(&dtl->lock);
>
> if (rc) {
> - read_unlock(&dtl_access_lock);
> + up_read(&dtl_access_lock);
> kmem_cache_free(dtl_cache, buf);
> }
>
> @@ -232,7 +232,7 @@ static void dtl_disable(struct dtl *dtl)
> dtl->buf = NULL;
> dtl->buf_entries = 0;
> spin_unlock(&dtl->lock);
> - read_unlock(&dtl_access_lock);
> + up_read(&dtl_access_lock);
> }
>
> /* file interface */
> diff --git a/arch/powerpc/platforms/pseries/lpar.c
> b/arch/powerpc/platforms/pseries/lpar.c
> index c1d8bee8f701..bb09990eec30 100644
> --- a/arch/powerpc/platforms/pseries/lpar.c
> +++ b/arch/powerpc/platforms/pseries/lpar.c
> @@ -169,7 +169,7 @@ struct vcpu_dispatch_data {
> */
> #define NR_CPUS_H NR_CPUS
>
> -DEFINE_RWLOCK(dtl_access_lock);
> +DECLARE_RWSEM(dtl_access_lock);
> static DEFINE_PER_CPU(struct vcpu_dispatch_data, vcpu_disp_data);
> static DEFINE_PER_CPU(u64, dtl_entry_ridx);
> static DEFINE_PER_CPU(struct dtl_worker, dtl_workers);
> @@ -463,7 +463,7 @@ static int dtl_worker_enable(unsigned long *time_limit)
> {
> int rc = 0, state;
>
> - if (!write_trylock(&dtl_access_lock)) {
> + if (!down_write_trylock(&dtl_access_lock)) {
> rc = -EBUSY;
> goto out;
> }
> @@ -479,7 +479,7 @@ static int dtl_worker_enable(unsigned long *time_limit)
> pr_err("vcpudispatch_stats: unable to setup workqueue for DTL
> processing\n");
> free_dtl_buffers(time_limit);
> reset_global_dtl_mask();
> - write_unlock(&dtl_access_lock);
> + up_write(&dtl_access_lock);
> rc = -EINVAL;
> goto out;
> }
> @@ -494,7 +494,7 @@ static void dtl_worker_disable(unsigned long *time_limit)
> cpuhp_remove_state(dtl_worker_state);
> free_dtl_buffers(time_limit);
> reset_global_dtl_mask();
> - write_unlock(&dtl_access_lock);
> + up_write(&dtl_access_lock);
> }
>
> static ssize_t vcpudispatch_stats_write(struct file *file, const char __user
> *p,
