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Re: [PATCH v3] dl-load: add memory barrier before updating the next
- From: Andreas Schwab <schwab at suse dot de>
- To: Maninder Singh <maninder1 dot s at samsung dot com>
- Cc: libc-alpha at sourceware dot org, triegel at redhat dot com, szabolcs dot nagy at arm dot com, pankaj dot m at samsung dot com, ajeet dot y at samsung dot com, a dot sahrawat at samsung dot com, lalit dot mohan at samsung dot com, akhilesh dot k at samsung dot com, hakbong5 dot lee at samsung dot com, Vaneet Narang <v dot narang at samsung dot com>
- Date: Mon, 03 Apr 2017 13:45:40 +0200
- Subject: Re: [PATCH v3] dl-load: add memory barrier before updating the next
- Authentication-results: sourceware.org; auth=none
- References: <CGME20170403113000epcas5p37d569cf71eda2d413cfab5e7f7e3591d@epcas5p3.samsung.com> <1491218925-19517-1-git-send-email-maninder1.s@samsung.com>
On Apr 03 2017, Maninder Singh <maninder1.s@samsung.com> wrote:
> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index a5318f9..03c6afb 100644
> --- a/elf/dl-load.c
> +++ b/elf/dl-load.c
> @@ -418,7 +418,10 @@ add_name_to_object (struct link_map *l, const char *name)
> newname->name = memcpy (newname + 1, name, name_len);
> newname->next = NULL;
> newname->dont_free = 0;
> - lastp->next = newname;
> + /* We need release memory order here because we need to synchronize
> + with other thread doing _dl_runtime_resolve which calls _dl_name_match_p
> + to traverse all names added to libname_list*/
> + atomic_store_release (&(lastp->next), newname);
Please remove the redundant parens.
> diff --git a/elf/dl-misc.c b/elf/dl-misc.c
> index 1e9a6ee..a26d6f6 100644
> --- a/elf/dl-misc.c
> +++ b/elf/dl-misc.c
> @@ -295,7 +295,10 @@ _dl_name_match_p (const char *name, const struct link_map *map)
> if (strcmp (name, runp->name) == 0)
> return 1;
> else
> - runp = runp->next;
> + /* We need to acquire memory order here because we need to synchronize
> + with other thread calling dlopen and adding new name to libname_list
> + through add_name_to_object */
> + runp = atomic_load_acquire(&(runp->next));
Likewise.
Andreas.
--
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."