From 40ddbbac7f16eb91f9f2bbc414f283102052ce14 Mon Sep 17 00:00:00 2001 From: John Ogness Date: Wed, 3 Mar 2021 11:15:15 +0100 Subject: [PATCH] mtd: mtdoops: synchronize kmsg_dumper The kmsg_dumper can be called from any context and CPU, possibly from multiple CPUs simultaneously. Since the writing of the buffer can occur from a later scheduled work queue, the oops buffer must be protected against simultaneous dumping. Use an atomic bit to mark when the buffer is protected. Release the protection in between setting the buffer and the actual writing in order for a possible panic (immediate write) to be written during the scheduling of a previous oops (delayed write). An atomic bit (rather than a spinlock) was chosen so that no scheduling or preemption side-effects would be introduced. The MTD kmsg_dumper may dump directly or it may be delayed (via scheduled work). Depending on the context, different MTD callbacks are used. For example, mtd_write() expects to be called in a non-atomic context and may take a mutex. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210303101528.29901-3-john.ogness@linutronix.de --- drivers/mtd/mtdoops.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c index 774970b..8bbfba4 100644 --- a/drivers/mtd/mtdoops.c +++ b/drivers/mtd/mtdoops.c @@ -52,6 +52,7 @@ static struct mtdoops_context { int nextcount; unsigned long *oops_page_used; + unsigned long oops_buf_busy; void *oops_buf; } oops_cxt; @@ -180,6 +181,9 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic) u32 *hdr; int ret; + if (test_and_set_bit(0, &cxt->oops_buf_busy)) + return; + /* Add mtdoops header to the buffer */ hdr = cxt->oops_buf; hdr[0] = cxt->nextcount; @@ -190,7 +194,7 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic) record_size, &retlen, cxt->oops_buf); if (ret == -EOPNOTSUPP) { printk(KERN_ERR "mtdoops: Cannot write from panic without panic_write\n"); - return; + goto out; } } else ret = mtd_write(mtd, cxt->nextpage * record_size, @@ -203,6 +207,8 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic) memset(cxt->oops_buf, 0xff, record_size); mtdoops_inc_counter(cxt); +out: + clear_bit(0, &cxt->oops_buf_busy); } static void mtdoops_workfunc_write(struct work_struct *work) @@ -276,8 +282,11 @@ static void mtdoops_do_dump(struct kmsg_dumper *dumper, if (reason == KMSG_DUMP_OOPS && !dump_oops) return; + if (test_and_set_bit(0, &cxt->oops_buf_busy)) + return; kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE, record_size - MTDOOPS_HEADER_SIZE, NULL); + clear_bit(0, &cxt->oops_buf_busy); if (reason != KMSG_DUMP_OOPS) { /* Panics must be written immediately */ @@ -394,6 +403,7 @@ static int __init mtdoops_init(void) return -ENOMEM; } memset(cxt->oops_buf, 0xff, record_size); + cxt->oops_buf_busy = 0; INIT_WORK(&cxt->work_erase, mtdoops_workfunc_erase); INIT_WORK(&cxt->work_write, mtdoops_workfunc_write); -- 2.7.4