powerpc/pseries: Fix dtl_access_lock to be a rw_semaphore

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")
Tested-by: Kajol Jain <kjain@linux.ibm.com>
Reviewed-by: Nysal Jan K.A <nysal@linux.ibm.com>
Reviewed-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20240819122401.513203-1-mpe@ellerman.id.au

diff --git a/arch/powerpc/include/asm/dtl.h b/arch/powerpc/include/asm/dtl.h
index d6f43d1..a5c21bc 100644 (file)
--- a/arch/powerpc/include/asm/dtl.h
+++ b/arch/powerpc/include/asm/dtl.h
@@ -1,8 +1,8 @@
 #ifndef _ASM_POWERPC_DTL_H
 #define _ASM_POWERPC_DTL_H
 
+#include <linux/rwsem.h>
 #include <asm/lppaca.h>
-#include <linux/spinlock_types.h>
 
 /*
  * Layout of entries in the hypervisor's dispatch trace log buffer.
@@ -35,7 +35,7 @@ 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 8cb9d36..f293588 100644 (file)
--- 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 0c428f1..6a415fe 100644 (file)
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -170,7 +170,7 @@ 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);
@@ -464,7 +464,7 @@ 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;
        }
@@ -480,7 +480,7 @@ 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;
        }
@@ -495,7 +495,7 @@ 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,