From: Nathan Lynch nathanl@linux.ibm.com
[ Upstream commit 9d6792ffe140240ae54c881cc4183f9acc24b4df ]
The drmem lmb list can have hundreds of thousands of entries, and unfortunately lookups take the form of linear searches. As long as this is the case, traversals have the potential to monopolize the CPU and provoke lockup reports, workqueue stalls, and the like unless they explicitly yield.
Rather than placing cond_resched() calls within various for_each_drmem_lmb() loop blocks in the code, put it in the iteration expression of the loop macro itself so users can't omit it.
Introduce a drmem_lmb_next() iteration helper function which calls cond_resched() at a regular interval during array traversal. Each iteration of the loop in DLPAR code paths can involve around ten RTAS calls which can each take up to 250us, so this ensures the check is performed at worst every few milliseconds.
Fixes: 6c6ea53725b3 ("powerpc/mm: Separate ibm, dynamic-memory data from DT format") Signed-off-by: Nathan Lynch nathanl@linux.ibm.com Reviewed-by: Christophe Leroy christophe.leroy@csgroup.eu Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20200813151131.2070161-1-nathanl@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/include/asm/drmem.h | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/include/asm/drmem.h b/arch/powerpc/include/asm/drmem.h index 9e516fe3daaba..668d8a121f1a0 100644 --- a/arch/powerpc/include/asm/drmem.h +++ b/arch/powerpc/include/asm/drmem.h @@ -12,6 +12,8 @@ #ifndef _ASM_POWERPC_LMB_H #define _ASM_POWERPC_LMB_H
+#include <linux/sched.h> + struct drmem_lmb { u64 base_addr; u32 drc_index; @@ -27,8 +29,22 @@ struct drmem_lmb_info {
extern struct drmem_lmb_info *drmem_info;
+static inline struct drmem_lmb *drmem_lmb_next(struct drmem_lmb *lmb, + const struct drmem_lmb *start) +{ + /* + * DLPAR code paths can take several milliseconds per element + * when interacting with firmware. Ensure that we don't + * unfairly monopolize the CPU. + */ + if (((++lmb - start) % 16) == 0) + cond_resched(); + + return lmb; +} + #define for_each_drmem_lmb_in_range(lmb, start, end) \ - for ((lmb) = (start); (lmb) < (end); (lmb)++) + for ((lmb) = (start); (lmb) < (end); lmb = drmem_lmb_next(lmb, start))
#define for_each_drmem_lmb(lmb) \ for_each_drmem_lmb_in_range((lmb), \