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authorThomas Richter <tmricht@linux.ibm.com>2019-11-22 16:43:15 +0100
committerVasily Gorbik <gor@linux.ibm.com>2019-11-30 10:52:46 +0100
commit247f265fa502e7b17a0cb0cc330e055a36aafce4 (patch)
tree21214ed7e37afff793993703a1e257357d3e6341 /arch/s390
parent7dd6b199df46e871e6e0d0cd7e4f71dc07dfd53c (diff)
s390/cpum_sf: Check for SDBT and SDB consistency
Each SBDT is located at a 4KB page and contains 512 entries. Each entry of a SDBT points to a SDB, a 4KB page containing sampled data. The last entry is a link to another SDBT page. When an event is created the function sequence executed is: __hw_perf_event_init() +--> allocate_buffers() +--> realloc_sampling_buffers() +---> alloc_sample_data_block() Both functions realloc_sampling_buffers() and alloc_sample_data_block() allocate pages and the allocation can fail. This is handled correctly and all allocated pages are freed and error -ENOMEM is returned to the top calling function. Finally the event is not created. Once the event has been created, the amount of initially allocated SDBT and SDB can be too low. This is detected during measurement interrupt handling, where the amount of lost samples is calculated. If the number of lost samples is too high considering sampling frequency and already allocated SBDs, the number of SDBs is enlarged during the next execution of cpumsf_pmu_enable(). If more SBDs need to be allocated, functions realloc_sampling_buffers() +---> alloc-sample_data_block() are called to allocate more pages. Page allocation may fail and the returned error is ignored. A SDBT and SDB setup already exists. However the modified SDBTs and SDBs might end up in a situation where the first entry of an SDBT does not point to an SDB, but another SDBT, basicly an SBDT without payload. This can not be handled by the interrupt handler, where an SDBT must have at least one entry pointing to an SBD. Add a check to avoid SDBTs with out payload (SDBs) when enlarging the buffer setup. Signed-off-by: Thomas Richter <tmricht@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Diffstat (limited to 'arch/s390')
-rw-r--r--arch/s390/kernel/perf_cpum_sf.c17
1 files changed, 15 insertions, 2 deletions
diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c
index cd9fb45eebd2..c07fdcd73726 100644
--- a/arch/s390/kernel/perf_cpum_sf.c
+++ b/arch/s390/kernel/perf_cpum_sf.c
@@ -193,7 +193,7 @@ static int realloc_sampling_buffer(struct sf_buffer *sfb,
unsigned long num_sdb, gfp_t gfp_flags)
{
int i, rc;
- unsigned long *new, *tail;
+ unsigned long *new, *tail, *tail_prev = NULL;
if (!sfb->sdbt || !sfb->tail)
return -EINVAL;
@@ -233,6 +233,7 @@ static int realloc_sampling_buffer(struct sf_buffer *sfb,
sfb->num_sdbt++;
/* Link current page to tail of chain */
*tail = (unsigned long)(void *) new + 1;
+ tail_prev = tail;
tail = new;
}
@@ -242,10 +243,22 @@ static int realloc_sampling_buffer(struct sf_buffer *sfb,
* issue, a new realloc call (if required) might succeed.
*/
rc = alloc_sample_data_block(tail, gfp_flags);
- if (rc)
+ if (rc) {
+ /* Undo last SDBT. An SDBT with no SDB at its first
+ * entry but with an SDBT entry instead can not be
+ * handled by the interrupt handler code.
+ * Avoid this situation.
+ */
+ if (tail_prev) {
+ sfb->num_sdbt--;
+ free_page((unsigned long) new);
+ tail = tail_prev;
+ }
break;
+ }
sfb->num_sdb++;
tail++;
+ tail_prev = new = NULL; /* Allocated at least one SBD */
}
/* Link sampling buffer to its origin */